THESE DOGS BY MEANS OF POSITIVE REINFORCEMENT BY ANNOUNCING VERBAL APPROVAL AND BITS OF FOOD EVENTUALLY LEARNED TO DISCRIMINATE BY SITTING AT CONCEALED SAMPLES OF PURE HEROIN HCL AND HEROIN HCL DILUTED AT 50% WITH MANNITOL, LACTOSE AND QUININE SULFATE. THE RESULTS OF THIS EXPERIMENT NOT ONLY PRODUCED DOGS THAT ADJUSTED TO LAW ENFORCEMENT USE BUT DEMONSTRATED THAT THEY CAN LEARN TO ASSOCIATE AN ACQUIRED BEHAVIOR WHEN STIMULATED BY A PRIMARY TARGET ODOR. SECONDARY TO LABORATORY OLFACTORY DISCRIMINATION SCHEDULES, THE DOGS LEARNED TO SEARCH FOR HEROIN HCL AT AIRPORTS, IN AUTOMOBILES, LUGGAGE, AND IN WAREHOUSES. EVENTUALLY THESE DOGS WERE TRANSFERRED TO SPECIAL U.S. LAW ENFORCEMENT AGENCIES FOR FIELD USE IN SCREENING ASSORTED TYPE OF CARGO FOR THE PRESENCE OF CONTRABAND. (AUTHOR ABSTRACT)