Problem in simple SQL request

Hi everybody! I have a little problem here.

I work under Microsoft Access 97.
I have 2 tables : A and B. The key of A are the same fields as the key of B (so, records are “equivalents”). Many records in A have no correspondant in B but all records in B have a correspondant in A.
I want to SELECT all records in A that have NO correspondant in B (of course, the classical “SELECT A.* FROM A,B WHERE A.key=B.key” is the exact contrary that I want!).
Can someone help, please ?
Thanks!