querying parameters for list box

[PaulA]

I have a listbox that I am using as a lookup tool on a form header. There are also parameter fields there whose sole purpose is so that any combination of paramaters entered will effect what records show in the list box. Clicking a record in the lisbox will then produce the appropriate record in the form.

I have not been successful in creating a query that will be appropriately effected by an combination of parameters (some with a value, some blank).

What is the best way to set up a query so this will work?

Thanks!