The usual way to check if the parameter is getting passed is using a tool like HttpHeaders, Firebug like David has mentioned.
Other than that (as I think your is a get request)
you should be able to see the parameters being passed in the URL itself (The URL once you click the submit button) Check to see if the parameters are getting passed there.
(In case of post a simple trick is to temporarily change the method to get - to see if the parameters being passed are correct. Of course if its Ajax there is no option but to fall back on Firebug and any http sniffer)