diff --git a/lib/webrat/core/elements/field.rb b/lib/webrat/core/elements/field.rb
index b81c38d..1a2088d 100644
--- a/lib/webrat/core/elements/field.rb
+++ b/lib/webrat/core/elements/field.rb
@@ -359,10 +359,16 @@ module Webrat
   protected
 
     def test_uploaded_file
-      if content_type
-        ActionController::TestUploadedFile.new(@value, content_type)
-      else
-        ActionController::TestUploadedFile.new(@value)
+      case Webrat.configuration.mode
+      when :rails
+        if content_type
+          ActionController::TestUploadedFile.new(@value, content_type)
+        else
+          ActionController::TestUploadedFile.new(@value)
+        end
+      when :merb
+        # TODO: support content_type
+        File.new(@value)
       end
     end
 
diff --git a/lib/webrat/merb_session.rb b/lib/webrat/merb_session.rb
index fcc9099..6c6ab94 100644
--- a/lib/webrat/merb_session.rb
+++ b/lib/webrat/merb_session.rb
@@ -5,6 +5,13 @@ gem "extlib"
 require "extlib"
 require "merb-core"
 
+begin
+  # Require Merb::Test::MultipartRequestHelper with multipart support.
+  require "merb-core/two-oh"
+rescue LoadError => e
+  # Maybe Merb got rid of this. We'll do more checking for multiparth support.
+end
+
 # HashWithIndifferentAccess = Mash
 
 module Webrat
@@ -37,13 +44,44 @@ module Webrat
       @response.status
     end
 
+    include Merb::Test::MultipartRequestHelper
+
     def do_request(url, data, headers, method)
-      @response = request(url,
-        :params => (data && data.any?) ? data : nil,
-        :headers => headers,
-        :method => method)
+      if method == "POST" && supports_multipart? && has_file?(data)
+        @response = multipart_post(url, data, :headers => headers)
+
+      elsif method == "PUT" && supports_multipart? && has_file?(data)
+        @response = multipart_put(url, data, :headers => headers)
+
+      else
+        @response = request(url,
+          :params => (data && data.any?) ? data : nil,
+          :headers => headers,
+          :method => method)
+      end
     end
 
+    protected
+
+      # multipart_post and multipart_put which use request to do their
+      # business through multipart_request. Older implementations of
+      # multipart_post and multipart_put use the controller directly.
+      def supports_multipart?
+        respond_to?(:multipart_request)
+      end
+
+      # Recursively search the data for a file attachment.
+      def has_file?(data)
+        data.each do |key, value|
+          if value.is_a?(Hash)
+            return has_file?(value)
+          else
+            return true if value.is_a?(File)
+          end
+        end
+        return false
+      end
+
   end
 end
 
diff --git a/spec/integration/merb/app/controllers/testing.rb b/spec/integration/merb/app/controllers/testing.rb
index 31ccbeb..14cba1b 100644
--- a/spec/integration/merb/app/controllers/testing.rb
+++ b/spec/integration/merb/app/controllers/testing.rb
@@ -4,6 +4,15 @@ class Testing < Application
     render
   end
 
+  def upload
+    case request.method
+    when :get then render
+    when :post then
+      uploaded_file = params[:uploaded_file]
+      render [uploaded_file[:filename], uploaded_file[:tempfile].class.name].inspect
+    end
+  end
+
   def submit_form
   end
 
diff --git a/spec/integration/merb/app/views/testing/upload.html.erb b/spec/integration/merb/app/views/testing/upload.html.erb
new file mode 100644
index 0000000..f750c55
--- /dev/null
+++ b/spec/integration/merb/app/views/testing/upload.html.erb
@@ -0,0 +1,9 @@
+<h1>Webrat Form</h1>
+
+<form action="/upload" method="post">
+  <label>
+    File
+    <input type="file" name="uploaded_file" />
+  </label>
+  <input type="submit" value="Upload">
+</form>
\ No newline at end of file
diff --git a/spec/integration/merb/config/router.rb b/spec/integration/merb/config/router.rb
index c57ec70..6ff8c3c 100644
--- a/spec/integration/merb/config/router.rb
+++ b/spec/integration/merb/config/router.rb
@@ -28,6 +28,7 @@
 Merb.logger.info("Compiling routes...")
 Merb::Router.prepare do
   match("/").to(:controller => "testing", :action => "show_form")
+  match("/upload").to(:controller => "testing", :action => "upload")
   match("/internal_redirect").to(:controller => "testing", :action => "internal_redirect")
   match("/external_redirect").to(:controller => "testing", :action => "external_redirect")
 end
diff --git a/spec/integration/merb/spec/webrat_spec.rb b/spec/integration/merb/spec/webrat_spec.rb
index bdaad20..6264dae 100644
--- a/spec/integration/merb/spec/webrat_spec.rb
+++ b/spec/integration/merb/spec/webrat_spec.rb
@@ -29,4 +29,11 @@ describe "Webrat" do
     response = visit "/external_redirect"
     response.status.should == 302
   end
+
+  it "should upload files" do
+    visit "/upload"
+    attach_file "File", __FILE__
+    response = click_button "Upload"
+    response.should contain(%(["webrat_spec.rb", "Tempfile"]))
+  end
 end
diff --git a/spec/private/merb/attaches_file_spec.rb b/spec/private/merb/attaches_file_spec.rb
new file mode 100644
index 0000000..5c17cfa
--- /dev/null
+++ b/spec/private/merb/attaches_file_spec.rb
@@ -0,0 +1,93 @@
+require File.expand_path(File.dirname(__FILE__) + '/../../spec_helper')
+
+describe "attach_file with merb" do
+  before do
+    Webrat.configuration.mode = :merb
+    @filename = __FILE__
+  end
+
+  it "should fail if no file field found" do
+    with_html <<-HTML
+      <html>
+      <form method="post" action="/widgets">
+      </form>
+      </html>
+    HTML
+    lambda { attach_file("Doc", "/some/path") }.should raise_error(Webrat::NotFoundError)
+  end
+
+  it "should submit empty strings for blank file fields" do
+    with_html <<-HTML
+      <html>
+      <form method="post" action="/widgets">
+        <input type="file" id="widget_file" name="widget[file]" />
+        <input type="submit" />
+      </form>
+      </html>
+    HTML
+    webrat_session.should_receive(:post).with("/widgets", { "widget" => { "file" => "" } })
+    click_button
+  end
+
+  it "should submit the attached file" do
+    with_html <<-HTML
+      <html>
+      <form method="post" action="/widgets">
+        <label for="widget_file">Document</label>
+        <input type="file" id="widget_file" name="widget[file]" />
+        <input type="submit" />
+      </form>
+      </html>
+    HTML
+    webrat_session.should_receive(:post).with { |path, params|
+      path.should == "/widgets"
+      params.should have_key("widget")
+      params["widget"].should have_key("file")
+      params["widget"]["file"].should be_an_instance_of(File)
+      params["widget"]["file"].path.should == @filename
+    }
+    attach_file "Document", @filename
+    click_button
+  end
+
+  it "should support collections" do
+    with_html <<-HTML
+      <html>
+      <form method="post" action="/widgets">
+        <label for="widget_file1">Document</label>
+        <input type="file" id="widget_file1" name="widget[files][]" />
+        <label for="widget_file2">Spreadsheet</label>
+        <input type="file" id="widget_file2" name="widget[files][]" />
+        <input type="submit" />
+      </form>
+      </html>
+    HTML
+    webrat_session.should_receive(:post).with { |path, params|
+      path.should == "/widgets"
+      params.should have_key("widget")
+      params["widget"].should have_key("files")
+      params["widget"]["files"][0].should be_an_instance_of(File)
+      params["widget"]["files"][0].path.should == @filename
+      params["widget"]["files"][1].should be_an_instance_of(File)
+      params["widget"]["files"][1].path.should == @filename
+    }
+    attach_file "Document", @filename
+    attach_file "Spreadsheet", @filename
+    click_button
+  end
+
+  xit "should allow the content type to be specified" do
+    with_html <<-HTML
+      <html>
+      <form method="post" action="/widgets">
+        <label for="person_picture">Picture</label>
+        <input type="file" id="person_picture" name="person[picture]" />
+        <input type="submit" />
+      </form>
+      </html>
+    HTML
+    ActionController::TestUploadedFile.should_receive(:new).with(@filename, "image/png").any_number_of_times
+    attach_file "Picture", @filename, "image/png"
+    click_button
+  end
+end
diff --git a/spec/private/merb/merb_session_spec.rb b/spec/private/merb/merb_session_spec.rb
index 25560f7..06b4b99 100644
--- a/spec/private/merb/merb_session_spec.rb
+++ b/spec/private/merb/merb_session_spec.rb
@@ -22,6 +22,25 @@ describe Webrat::MerbSession do
     end
   end
 
+  %w{post put}.each do |request_method|
+    it "should call do request with method #{request_method.upcase} with a file attachment" do
+      session = Webrat::MerbSession.new
+      response = OpenStruct.new
+      response.status = 200
+
+      file = File.new(__FILE__)
+      session.should_receive(:request).with { |path, env|
+        path.should == "url"
+        env[:method].should == request_method.upcase
+        env[:headers].should be_nil
+        env[:input].should be_an_instance_of(StringIO)
+        env["CONTENT_LENGTH"].should be_an_instance_of(Fixnum)
+        env["CONTENT_TYPE"].should match(/multipart.*boundary/)
+      }.and_return(response)
+      session.send(request_method, 'url', { :file => file }, nil)
+    end
+  end
+
   context "a session with a response" do
     before do
       @session = Webrat::MerbSession.new