How are you setting the content-type? In the two ways I tried, mongrel never added the charset...
1) Setting headers['Content-Type'] in the rails action.
$ cat app/controllers/test_controller.rb class TestController < ApplicationController def test headers['Content-Type'] = 'audio/x-scpls' render :text => 'hi', :layout => false end end $ lwp-request -d -e http://localhost:3000/test ... Content-Type: audio/x-scpls ...
2) Serving a file and having DirHandler serve the file, and using DirHandler.add_mime_type to return the right mime-type.
$ cat config/mongrel.conf DirHandler.add_mime_type '.pls', 'audio/x-scpls' $ lwp-request -e http://localhost:3000/test.pls ... Content-Type: audio/x-scpls ...