ajax for loading my drop down menus?

ajax for loading my drop down menus?

I've used the ajax function to load in data like "click the submit button, ajax executes output.php and throws in back into a div tag in theform.php." 

But what if I have a multiple dropdown menus that submit the form and need to be reloaded depending on the previous dropdown menu's value? How would I set up the ajax so those are loaded without a refresh?


Thanks