Thanks much for your response. I tried your suggestion, but I got an error indicating that onreadystatechange is not a function (which means it cannot recognize a parameter in the way you suggested passing it). As far as not needing a parameter because a different button is clicked and therefore a different response is coming back from the server -- no, the reason I need a parameter is that I have mutliple DOM elements with buttons on them and I need to remember which element generated the request so that on return from the server I can expand the particular element on the page (with the data I am getting back from the server). I am not simply doing an innerhtml rewrite of an element on the page, as many ajax applications do. Instead, I am expanding (appending to) a specific DOM element based on which one was clicked.