diff --git a/app/helpers/comment_helper.rb b/app/helpers/comment_helper.rb
index 6311169..4c8760d 100644
--- a/app/helpers/comment_helper.rb
+++ b/app/helpers/comment_helper.rb
@@ -22,6 +22,12 @@ module CommentHelper
     title
   end
 
+  def comment_extra_contents(comment)
+    @plugins.dispatch(:comment_extra_contents, comment).collect do |extra_content|
+      extra_content.kind_of?(Proc) ? self.instance_eval(&extra_content) : extra_content
+    end.join('\n')
+  end
+
   def comment_actions(comment)
     url = url_for(:profile => profile.identifier, :controller => :comment, :action => :check_actions, :id => comment.id)
     links = links_for_comment_actions(comment)
diff --git a/app/views/content_viewer/view_page.rhtml b/app/views/content_viewer/view_page.rhtml
index f3f83dc..f57ea88 100644
--- a/app/views/content_viewer/view_page.rhtml
+++ b/app/views/content_viewer/view_page.rhtml
@@ -84,6 +84,8 @@
 
 <%= display_source_info(@page) %>
 
+<%= @plugins.dispatch(:article_extra_contents, @page).collect { |content| instance_eval(&content) }.join("") %>
+
 <div class="comments" id="comments_list">
 
   <% if @page.accept_comments? || @comments_count > 0 %>
diff --git a/lib/noosfero/plugin.rb b/lib/noosfero/plugin.rb
index eed5ac5..4927c87 100644
--- a/lib/noosfero/plugin.rb
+++ b/lib/noosfero/plugin.rb
@@ -349,6 +349,12 @@ class Noosfero::Plugin
     []
   end
 
+  # -> Adds adicional content to article
+  # returns = lambda block that creates html code
+  def article_extra_contents(article)
+    nil
+  end
+
   # -> Adds fields to the signup form
   # returns = lambda block that creates html code
   def signup_extra_contents
diff --git a/plugins/mark_comment_as_read/controllers/mark_comment_as_read_plugin_profile_controller.rb b/plugins/mark_comment_as_read/controllers/mark_comment_as_read_plugin_profile_controller.rb
new file mode 100644
index 0000000..9f2fde9
--- /dev/null
+++ b/plugins/mark_comment_as_read/controllers/mark_comment_as_read_plugin_profile_controller.rb
@@ -0,0 +1,17 @@
+class MarkCommentAsReadPluginProfileController < ProfileController
+
+  append_view_path File.join(File.dirname(__FILE__) + '/../views')
+
+  def mark_as_read
+    comment = Comment.find(params[:id])
+    comment.mark_as_read(user)
+    render :text => {'ok' => true}.to_json, :content_type => 'application/json'
+  end
+
+  def mark_as_not_read
+    comment = Comment.find(params[:id])
+    comment.mark_as_not_read(user)
+    render :text => {'ok' => true}.to_json, :content_type => 'application/json'
+  end
+
+end
diff --git a/plugins/mark_comment_as_read/db/migrate/20130509184338_create_mark_comment_as_read_plugin.rb b/plugins/mark_comment_as_read/db/migrate/20130509184338_create_mark_comment_as_read_plugin.rb
new file mode 100644
index 0000000..7d8f789
--- /dev/null
+++ b/plugins/mark_comment_as_read/db/migrate/20130509184338_create_mark_comment_as_read_plugin.rb
@@ -0,0 +1,13 @@
+class CreateMarkCommentAsReadPlugin < ActiveRecord::Migration
+  def self.up
+    create_table :mark_comment_as_read_plugin do |t|
+      t.integer :comment_id
+      t.integer :person_id
+    end
+    add_index :mark_comment_as_read_plugin, [:comment_id, :person_id], :unique => true
+  end
+
+  def self.down
+    drop_table :mark_comment_as_read_plugin
+  end
+end
diff --git a/plugins/mark_comment_as_read/lib/mark_comment_as_read_plugin.rb b/plugins/mark_comment_as_read/lib/mark_comment_as_read_plugin.rb
new file mode 100644
index 0000000..a816e21
--- /dev/null
+++ b/plugins/mark_comment_as_read/lib/mark_comment_as_read_plugin.rb
@@ -0,0 +1,45 @@
+require_dependency 'mark_comment_as_read_plugin/ext/comment'
+
+class MarkCommentAsReadPlugin < Noosfero::Plugin
+
+  def self.plugin_name
+    "MarkCommentAsReadPlugin"
+  end
+
+  def self.plugin_description
+    _("Provide a button to mark a comment as read.")
+  end
+
+  def js_files
+    'mark_comment_as_read.js'
+  end
+
+  def stylesheet?
+    true
+  end
+
+  def comment_actions(comment)
+    lambda do
+      [{:link => link_to_function(_('Mark as not read'), 'toggle_comment_read(this, %s, false);' % url_for(:controller => 'mark_comment_as_read_plugin_profile', :profile => profile.identifier, :action => 'mark_as_not_read', :id => comment.id).to_json, :class => 'comment-footer comment-footer-link comment-footer-hide comment-action-extra', :style => 'display: none', :id => "comment-action-mark-as-not-read-#{comment.id}")},
+      {:link => link_to_function(_('Mark as read'), 'toggle_comment_read(this, %s, true);' % url_for(:controller => 'mark_comment_as_read_plugin_profile', :profile => profile.identifier, :action => 'mark_as_read', :id => comment.id).to_json, :class => 'comment-footer comment-footer-link comment-footer-hide comment-action-extra', :style => 'display: none', :id => "comment-action-mark-as-read-#{comment.id}")}] if user
+    end
+  end
+
+  def check_comment_actions(comment)
+    lambda do
+      if user
+        comment.marked_as_read?(user) ? "#comment-action-mark-as-not-read-#{comment.id}" : "#comment-action-mark-as-read-#{comment.id}"
+      end
+    end
+  end
+
+  def article_extra_contents(article)
+    lambda do
+      if user
+        ids = article.comments.marked_as_read(user).collect { |comment| comment.id}
+        "<script type=\"text/javascript\">mark_comments_as_read(#{ids.to_json});</script>" if !ids.empty?
+      end
+    end
+  end
+
+end
diff --git a/plugins/mark_comment_as_read/lib/mark_comment_as_read_plugin/ext/comment.rb b/plugins/mark_comment_as_read/lib/mark_comment_as_read_plugin/ext/comment.rb
new file mode 100644
index 0000000..15ec814
--- /dev/null
+++ b/plugins/mark_comment_as_read/lib/mark_comment_as_read_plugin/ext/comment.rb
@@ -0,0 +1,24 @@
+require_dependency 'comment'
+
+class Comment
+
+  has_many :read_comments, :class_name => 'MarkCommentAsReadPlugin::ReadComments'
+  has_many :people, :through => :read_comments
+
+  def mark_as_read(person)
+    people << person
+  end
+
+  def mark_as_not_read(person)
+    people.delete(person)
+  end
+
+  def marked_as_read?(person)
+    person && people.find(:first, :conditions => {:id => person.id})
+  end
+
+  def self.marked_as_read(person)
+    find(:all, :joins => [:read_comments], :conditions => {:author_id => person.id})
+  end
+
+end
diff --git a/plugins/mark_comment_as_read/lib/mark_comment_as_read_plugin/read_comments.rb b/plugins/mark_comment_as_read/lib/mark_comment_as_read_plugin/read_comments.rb
new file mode 100644
index 0000000..9ce10b7
--- /dev/null
+++ b/plugins/mark_comment_as_read/lib/mark_comment_as_read_plugin/read_comments.rb
@@ -0,0 +1,7 @@
+class MarkCommentAsReadPlugin::ReadComments < Noosfero::Plugin::ActiveRecord
+  set_table_name 'mark_comment_as_read_plugin'
+  belongs_to :comment
+  belongs_to :person
+
+  validates_presence_of :comment, :person
+end
diff --git a/plugins/mark_comment_as_read/public/mark_comment_as_read.js b/plugins/mark_comment_as_read/public/mark_comment_as_read.js
new file mode 100644
index 0000000..16cfc4f
--- /dev/null
+++ b/plugins/mark_comment_as_read/public/mark_comment_as_read.js
@@ -0,0 +1,28 @@
+function mark_comments_as_read(comments) {
+  jQuery(document).ready(function($) {
+    for(var i=0; i<comments.length; i++) {
+      $comment = jQuery('#comment-'+comments[i]);
+      $comment.find('.comment-content').first().addClass('comment-mark-read');
+    }
+  });
+}
+
+function toggle_comment_read(button, url, mark) {
+  var $ = jQuery;
+  var $button = $(button);
+  $button.addClass('comment-button-loading');
+  $.post(url, function(data) {
+    if (data.ok) {
+      var $comment = $button.closest('.article-comment');
+      var $content = $comment.find('.comment-content').first();
+      if(mark)
+        $content.addClass('comment-mark-read');
+      else
+        $content.removeClass('comment-mark-read');
+      $button.hide();
+      $button.removeClass('comment-button-loading');
+      return;
+    }
+  });
+}
+
diff --git a/plugins/mark_comment_as_read/public/style.css b/plugins/mark_comment_as_read/public/style.css
new file mode 100644
index 0000000..7f58961
--- /dev/null
+++ b/plugins/mark_comment_as_read/public/style.css
@@ -0,0 +1,3 @@
+.article-comments-list .comment-mark-read .comment-text, .article-comments-list .comment-mark-read h4, .article-comments-list .comment-mark-read .comment-picture {
+  opacity: 0.2;
+}
diff --git a/plugins/mark_comment_as_read/test/functional/mark_comment_as_read_plugin_profile_controller_test.rb b/plugins/mark_comment_as_read/test/functional/mark_comment_as_read_plugin_profile_controller_test.rb
new file mode 100644
index 0000000..777dcb0
--- /dev/null
+++ b/plugins/mark_comment_as_read/test/functional/mark_comment_as_read_plugin_profile_controller_test.rb
@@ -0,0 +1,33 @@
+require File.dirname(__FILE__) + '/../../../../test/test_helper'
+require File.dirname(__FILE__) + '/../../controllers/mark_comment_as_read_plugin_profile_controller'
+
+# Re-raise errors caught by the controller.
+class MarkCommentAsReadPluginProfileController; def rescue_action(e) raise e end; end
+
+class MarkCommentAsReadPluginProfileControllerTest < ActionController::TestCase
+  def setup
+    @controller = MarkCommentAsReadPluginProfileController.new
+    @request    = ActionController::TestRequest.new
+    @response   = ActionController::TestResponse.new
+    @profile = create_user('profile').person
+    @article = TinyMceArticle.create!(:profile => @profile, :name => 'An article')
+    @comment = Comment.new(:source => @article, :author => @profile, :body => 'test')
+    @comment.save!
+    login_as(@profile.identifier)
+    environment = Environment.default
+    environment.enable_plugin(MarkCommentAsReadPlugin)
+    self.stubs(:user).returns(@profile)
+  end
+
+  attr_reader :profile, :comment
+
+  should 'mark comment as read' do
+    xhr :post, :mark_as_read, :profile => profile.identifier, :id => comment.id
+    assert_match /\{\"ok\":true\}/, @response.body
+  end
+
+  should 'mark comment as not read' do
+    xhr :post, :mark_as_not_read, :profile => profile.identifier, :id => comment.id
+    assert_match /\{\"ok\":true\}/, @response.body
+  end
+end
diff --git a/plugins/mark_comment_as_read/test/unit/mark_comment_as_read_plugin/comment_test.rb b/plugins/mark_comment_as_read/test/unit/mark_comment_as_read_plugin/comment_test.rb
new file mode 100644
index 0000000..8c41450
--- /dev/null
+++ b/plugins/mark_comment_as_read/test/unit/mark_comment_as_read_plugin/comment_test.rb
@@ -0,0 +1,38 @@
+require File.dirname(__FILE__) + '/../../../../../test/test_helper'
+
+class MarkCommentAsReadPlugin::CommentTest < ActiveSupport::TestCase
+
+  def setup
+    @person = create_user('user').person
+    @article = TinyMceArticle.create!(:profile => @person, :name => 'An article')
+    @comment = Comment.create!(:title => 'title', :body => 'body', :author_id => @person.id, :source => @article)
+  end
+
+  should 'mark comment as read' do
+    assert !@comment.marked_as_read?(@person)
+    @comment.mark_as_read(@person)
+    assert @comment.marked_as_read?(@person)
+  end
+
+  should 'do not mark a comment as read again' do
+    @comment.mark_as_read(@person)
+    assert_raise ActiveRecord::StatementInvalid do
+      @comment.mark_as_read(@person)
+    end
+  end
+
+  should 'mark comment as not read' do
+    @comment.mark_as_read(@person)
+    assert @comment.marked_as_read?(@person)
+    @comment.mark_as_not_read(@person)
+    assert !@comment.marked_as_read?(@person)
+  end
+
+  should 'return comments marked as read for a user' do
+    person2 = create_user('user2').person
+    @comment.mark_as_read(@person)
+    assert_equal [], @article.comments.marked_as_read(@person) - [@comment]
+    assert_equal [], @article.comments.marked_as_read(person2)
+  end
+
+end
diff --git a/plugins/mark_comment_as_read/test/unit/mark_comment_as_read_test.rb b/plugins/mark_comment_as_read/test/unit/mark_comment_as_read_test.rb
new file mode 100644
index 0000000..5a1c8fd
--- /dev/null
+++ b/plugins/mark_comment_as_read/test/unit/mark_comment_as_read_test.rb
@@ -0,0 +1,87 @@
+require File.dirname(__FILE__) + '/../../../../test/test_helper'
+
+class MarkCommentAsReadPluginTest < ActiveSupport::TestCase
+
+  include ActionView::Helpers::TagHelper
+  include NoosferoTestHelper
+
+  def setup
+    @plugin = MarkCommentAsReadPlugin.new
+    @person = create_user('user').person
+    @article = TinyMceArticle.create!(:profile => @person, :name => 'An article')
+    @comment = Comment.create!(:source => @article, :author => @person, :body => 'test')
+    self.stubs(:user).returns(@person)
+    self.stubs(:profile).returns(@person)
+  end
+
+  attr_reader :plugin, :comment
+
+  should 'show link when person is logged in' do
+    action = @plugin.comment_actions(@comment)
+    link = self.instance_eval(&action)
+    assert link
+  end
+
+  should 'do not show link when person is not logged in' do
+    self.stubs(:user).returns(nil)
+    action = @plugin.comment_actions(@comment)
+    link = self.instance_eval(&action)
+    assert !link
+  end
+
+  should 'return actions when comment is not read' do
+    action = @plugin.comment_actions(@comment)
+    links = self.instance_eval(&action)
+    assert_equal 2, links.size
+  end
+
+  should 'return actions when comment is read' do
+    @comment.mark_as_read(@person)
+    action = @plugin.comment_actions(@comment)
+    links = self.instance_eval(&action)
+    assert_equal 2, links.size
+  end
+
+  should 'do not return any id when user is not logged in' do
+    self.stubs(:user).returns(nil)
+    action = @plugin.check_comment_actions(@comment)
+    id = self.instance_eval(&action)
+    assert !id
+  end
+
+  should 'return id of mark as not read link when comment is read' do
+    @comment.mark_as_read(@person)
+    action = @plugin.check_comment_actions(@comment)
+    id = self.instance_eval(&action)
+    assert_equal "#comment-action-mark-as-not-read-#{@comment.id}", id
+  end
+
+  should 'return id of mark as read link when comment is not read' do
+    action = @plugin.check_comment_actions(@comment)
+    id = self.instance_eval(&action)
+    assert_equal "#comment-action-mark-as-read-#{@comment.id}", id
+  end
+
+  should 'return javascript to mark comment as read' do
+    @comment.mark_as_read(@person)
+    content = @plugin.article_extra_contents(@article)
+    assert self.instance_eval(&content)
+  end
+
+  should 'do not return extra content if comment is not marked as read' do
+    content = @plugin.article_extra_contents(@article)
+    assert !self.instance_eval(&content)
+  end
+
+  should 'do not return extra content if user is not logged in' do
+    @comment.mark_as_read(@person)
+    self.stubs(:user).returns(nil)
+    content = @plugin.article_extra_contents(@article)
+    assert !self.instance_eval(&content)
+  end
+
+  def link_to_function(content, url, options = {})
+    link_to(content, url, options)
+  end
+
+end
diff --git a/test/unit/plugin_test.rb b/test/unit/plugin_test.rb
index 80b38e7..50cc012 100644
--- a/test/unit/plugin_test.rb
+++ b/test/unit/plugin_test.rb
@@ -496,4 +496,29 @@ class PluginTest < ActiveSupport::TestCase
     end
   end
 
+  should 'comment_actions be nil if the comment is nil' do
+    class SomePlugin < Noosfero::Plugin; end
+    plugin = SomePlugin.new
+    assert_nil plugin.comment_actions(nil)
+  end
+
+  should 'comment_actions be nil by default' do
+    class SomePlugin < Noosfero::Plugin; end
+    plugin = SomePlugin.new
+    assert_nil plugin.comment_actions(Comment.new)
+  end
+
+  should 'check_comment_actions be an empty array if the comment is nil' do
+    class SomePlugin < Noosfero::Plugin; end
+    plugin = SomePlugin.new
+    assert_equal [], plugin.check_comment_actions(nil)
+  end
+
+
+  should 'check_comment_actions be  an empty array by default' do
+    class SomePlugin < Noosfero::Plugin; end
+    plugin = SomePlugin.new
+    assert_equal [], plugin.check_comment_actions(Comment.new)
+  end
+
 end
--
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