Deleting Rows From Joined Tables

I am using the following query to identify rows in one table that have no match in another:

SELECT MAS.MASID
FROM MAS LEFT JOIN IVT ON MAS.Field1=IVT.Field1
WHERE ((IVT.IVTID) Is Null);


MAS is one file with MASID as the key.
IVT is the other file with IVTID as the key

This provides me a list of the rows in MAS with no match in IVT.

I now want to delete these rows in MAS so we can process the other fields in the table.

what is the syntax for the delete statement? I can't get the join to fit in correctly.

Help!