Sending variables from PHP to ASP

We're trying to intergrate a PHP mailing script on an NT server. The server has an ASP script that we need to send some variables to from a PHP page. I've been using the header command to redirect the browser to the ASP page and put the variables in the URL. The problem is that the variables are too long and get cut off in the URL. Is there another way to send variables from one page to another? Thanks, Jason