“Reasonable minds frequently may differ on the question whether a particular affidavit establishes probable cause” and “great deference” is to be given to magistrate’s determination of the matter. However, a plaintiff may challenge the presumption of validity afforded a warrant where the issuing judge was misled by information contained in the affidavit that the affiant either (1) knew was false or (2) would have known was false had he not recklessly disregarded the truth. The purpose of this column is to discuss the liability that a law enforcement officer may incur in such situations under 42 U.S.C. 1983, which is one of the primary federal statutes under which lawsuits are filed against state and local law enforcement officers.