[AccessD] SQL ANDs

Hi Folks

I have a report query that has a WHERE followered by one or a number of ANDs. The components of the ANDs reference text boxes on a form each of which may or may not be populated. How can I get it to negate one or a number of the ANDs if the target box is Null? At the moment if any one of the AND components is Null no records are returned. I've played around with IIF to test each box first but no luck so far....

Thanks

Martin