Richard, I have my own table that I am working on these days.  In this 'people table,' I have 6 fields: ID number, status, prefix, first name, middle initial and last name. 11 records so far. I'd like to set up a query for null values.
I can see that 7 out of 11 records are missing the middle initial. I set up the query with the 6 fields, based on a table. All the Show boxes are marked. I run it and all 11 records appear. I save the query.  
Then I type in "IsNull" for Criteria in the middle initial field (Design View). When I run the query again, no records appear.  I expected 7 records to appear - those without a middle initial.  What's wrong with this picture?