MOUSE KILLING BY RATS WAS SUPPRESSED IN THE PRESENCE OF A BUZZER TONE WHICH HAD PREVIOUSLY BEEN ASSOCIATED WITH PAINFUL ELECTRIC SHOCK. PRESENCE OF A MOUSE DURING ACQUISITION OF CONDITIONED SUPPRESSION DID NOT ALTER TEST PERFORMANCE OR EXTINCTION RATE OF RATS GIVEN FORWARD-CONDITIONING TRAINING. RATS WHICH SHOWED CONDITIONED SUPPRESSION TO THE BUZZER ALWAYS KILLED IMMEDIATELY WHEN SHOCK WAS PRESENTED. THUS, CS AND UCS HAD OPPOSITE EFFECTS ON BEHAVIOR. RATS TRAINED BY A PSEUDOCONDITIONING PROCEDURE SHOWED SOME SUPPRESSION OF KILLING, BUT THEIR TEST PERFORMANCE WAS UNRELATED TO THE PRESENCE OF THE BUZZER. (PsycINFO Database Record (c) 2006 APA, all rights reserved)