diff --git a/doc/api/issues.md b/doc/api/issues.md
index b782cec975b..025c6e50bb3 100644
--- a/doc/api/issues.md
+++ b/doc/api/issues.md
@@ -1,7 +1,7 @@
 ## List issues
 
 Get all issues created by authenticed user. This function takes pagination parameters
-`page` and `per_page` to get a list of issues.
+`page` and `per_page` to restrict the list of issues.
 
 ```
 GET /issues
diff --git a/doc/api/merge_requests.md b/doc/api/merge_requests.md
index 525c55d12c2..633aca78951 100644
--- a/doc/api/merge_requests.md
+++ b/doc/api/merge_requests.md
@@ -1,6 +1,7 @@
 ## List merge requests
 
-Get all MR for this project.
+Get all merge requests for this project. This function takes pagination parameters
+`page` and `per_page` to restrict the list of merge requests.
 
 ```
 GET /projects/:id/merge_requests
@@ -40,9 +41,16 @@ Parameters:
 ]
 ```
 
-## Show MR
+Return values:
 
-Show information about MR.
++ `200 Ok` on success and the list of merge requests
++ `401 Unauthorized` if user is not authenticated
++ `404 Not Found` if project ID not found
+
+
+## Get single MR
+
+Shows information about a single merge request.
 
 ```
 GET /projects/:id/merge_request/:merge_request_id
@@ -81,10 +89,16 @@ Parameters:
 }
 ```
 
+Return values:
+
++ `200 Ok` on success and the single merge request
++ `401 Unauthorized` if user is not authenticated
++ `404 Not Found` if project ID or merge request ID not found
+
 
 ## Create MR
 
-Create MR.
+Creates a new merge request.
 
 ```
 POST /projects/:id/merge_requests
@@ -126,9 +140,18 @@ Parameters:
 }
 ```
 
+Return values:
+
++ `201 Created` on success and the created merge request
++ `400 Bad Request` if one of the required attributes is missing
++ `401 Unauthorize` if user is not authenticated or not allowed
++ `403 Forbidden` if user is not allowed to create a merge request
++ `404 Not Found` if project ID not found or something else fails
+
+
 ## Update MR
 
-Update MR. You can change branches, title, or even close the MR.
+Updates an existing merge request. You can change branches, title, or even close the MR.
 
 ```
 PUT /projects/:id/merge_request/:merge_request_id
@@ -172,9 +195,18 @@ Parameters:
     }
 }
 ```
+
+Return values:
+
++ `200 Ok` on success and the updated merge request
++ `401 Unauthorize` if user is not authenticated or not allowed
++ `403 Forbidden` if user is not allowed to update the merge request
++ `404 Not Found` if project ID or merge request ID not found
+
+
 ## Post comment to MR
 
-Post comment to MR
+Adds a comment to a merge request.
 
 ```
 POST /projects/:id/merge_request/:merge_request_id/comments
@@ -183,10 +215,9 @@ POST /projects/:id/merge_request/:merge_request_id/comments
 Parameters:
 
 + `id` (required) - The ID of a project
-+ `merge_request_id` (required) - ID of MR
++ `merge_request_id` (required) - ID of merge request
 + `note` (required) - Text of comment
 
-Will return created note with status `201 Created` on success, or `404 Not found` on fail.
 
 ```json
 {
@@ -201,3 +232,10 @@ Will return created note with status `201 Created` on success, or `404 Not found
     "note":"text1"
 }
 ```
+
+Return values:
+
++ `201 Created` on success and the new comment
++ `400 Bad Request` if the required attribute note is not given
++ `401 Unauthorized` if user is not authenticated
++ `404 Not Found` if project ID or merge request ID not found
diff --git a/lib/api/merge_requests.rb b/lib/api/merge_requests.rb
index 4b28094f1a4..76cf8154bf8 100644
--- a/lib/api/merge_requests.rb
+++ b/lib/api/merge_requests.rb
@@ -69,6 +69,10 @@ module Gitlab
       post ":id/merge_requests" do
         authorize! :write_merge_request, user_project
 
+        bad_request!(:source_branch) unless params[:source_branch].present?
+        bad_request!(:target_branch) unless params[:target_branch].present?
+        bad_request!(:title) unless params[:title].present?
+
         attrs = attributes_for_keys [:source_branch, :target_branch, :assignee_id, :title]
         merge_request = user_project.merge_requests.new(attrs)
         merge_request.author = current_user
@@ -121,6 +125,8 @@ module Gitlab
       #   POST /projects/:id/merge_request/:merge_request_id/comments
       #
       post ":id/merge_request/:merge_request_id/comments" do
+        bad_request!(:note) unless params[:note].present?
+
         merge_request = user_project.merge_requests.find(params[:merge_request_id])
         note = merge_request.notes.new(note: params[:note], project_id: user_project.id)
         note.author = current_user
@@ -128,9 +134,6 @@ module Gitlab
         if note.save
           present note, with: Entities::MRNote
         else
-          if note.errors[:note].any?
-            bad_request!(:note)
-          end
           not_found!
         end
       end
diff --git a/spec/requests/api/merge_requests_spec.rb b/spec/requests/api/merge_requests_spec.rb
index 8de06c33394..e7af056af8e 100644
--- a/spec/requests/api/merge_requests_spec.rb
+++ b/spec/requests/api/merge_requests_spec.rb
@@ -64,6 +64,12 @@ describe Gitlab::API do
         title: "Test merge_request", source_branch: "stable", author: user
       response.status.should == 400
     end
+
+    it "should return 400 when title is missing" do
+      post api("/projects/#{project.id}/merge_requests", user),
+        target_branch: 'master', source_branch: 'stable'
+      response.status.should == 400
+    end
   end
 
   describe "PUT /projects/:id/merge_request/:merge_request_id to close MR" do
@@ -82,7 +88,6 @@ describe Gitlab::API do
     end
   end
 
-
   describe "PUT /projects/:id/merge_request/:merge_request_id" do
     it "should return merge_request" do
       put api("/projects/#{project.id}/merge_request/#{merge_request.id}", user), title: "New title"