Using XMLHttpRequest() To Pass Multiple Values?

Maybe this has been tackled in another post but I couldn't find it through some searching so here goes...I'm using an Ajaxy method to update an administrative form and what I would like to do is update multiple text fields when the onchange fires from a dropdown list. Basically, I pull up a business name in the dropdown and fields for address, city, postal, phone, fax, etc... is updated.

The script that I've cobbled together is really good at updating one item via the XMLHttpRequest() responseText property and I could send a string of variables that I could break out into an array to loop into the innerHTML of each item but I was hoping there would be a more sophisticated way to do it.Is there a way to pass a responseArray instead of just a string of text?