What ADO finction is used to test to see if a query excuted on a database returned null?

It is field by field. Each field has a value, that is a variant.
See http://msdn.microsoft.com/en-us/library/windows/desktop/ms675309(v=vs.85).aspx[^]
See also: http://msdn.microsoft.com/en-us/library/windows/desktop/ms677568(v=vs.85).aspx[^]

The variant type (explained in http://msdn.microsoft.com/en-us/library/cc237865.aspx[^]) will be VT_NULL for NULL database fields.

Hope this helps,

Pablo.