A quick follow up. In short the problem was that Mechanize and LWP do not interpret client side java script. There is a module that was just released that hooks into mechanize: WWW::Scripter::Plugin::JavaScript But it is very new and not yet recognized by the Mechanize owner. In the end the java script was rather simplistic. I added two lines to the form call, adding values for the two hidden variables and the server side CGI did the rest.