You would use Is Null and Is Not Null in query expressions and SQL WHERE clauses. IsNull(), on the other hand, is a Visual Basic for Applications (VBA) function and would be used only in VBA modules.

The mice in which exons 5–8 of the CRHR1 were replaced with a PCK-neomycin-resistant cassette (CRHR1 null) 7 and their wild ... The residual fat and tissue is not a confound for the subsequent ...