You need to repeat the column name for each Boolean AND operation.  In SQL it
would be:

WHERE YourColumn <> "AB"
AND YourColumn <> "CD"
AND YourColumn <> "DS"

In query design view you'd add the column to the grid once for each value
you need to exclude, uncheck the 'show' check box for all but the first and
in the criteria row of the first put the <> "AB", in that of the second <>
"CD" and so on.

Using a NOT IN operation with a value list as Kerry suggests is simpler,
however.

Ken Sheridan
Stafford, England