program a change event on dropdown list

So, What I want is a help...

I have 3 mysql tables: province, district a healthfacility with the relations: The province have one or more districts and the health facility is located on the district.

What I want to do, is following next:

"I want to make a php page where the system user can select a province, district and heathfacility on the same page...and is not difficulty for me to distplay this information in a dropdown list. But what is difficulty for me is to program a change event on dropdown list where, when I select a province on a province dropdown list at district dropdown list must only apear the distrit of the select province. And this is applied for the healthfacility".

Is there everyone that can help me, solving this issue?

Sorry for my english. My official language is Portuguese, but i think the ideia is there...

It sounds like you'll need to use AJAX to make your database calls without reloading the page.