THE SUBJECTS WERE 34 INMATES (17 PSYCHOPATHS AND 17 NONPSYCHOPATHS) OF THE MATSQUI MEDIUM SECURITY INSTITUTION IN BRITISH COLUMBIA. DEGREES OF PSYCHOPATHY FOR THE SUBJECTS WERE OBTAINED USING A GLOBAL ASSESSMENT SCALE. THE SUBJECTS' HEART RATE AND SKIN CONDUCTANCE WERE RECORDED WHILE THEY PLAYED IN A MIXED-MOTIVE GAME SITUATION. ON EACH TRIAL PLAYER A HAD TO CHOOSE THE INTENSITY OF SHOCK TO BE DELIVERED TO HIMSELF AND TO PLAYER B. B THEN WAS GIVEN A CHANCE TO RETALIATE, ALTHOUGH HIS CHOICES WERE ACTUALLY OVERRIDDEN BY THE EXPERIMENTER. A 10-SECOND TONE PRECEDED DELIVERY OF A SHOCK TO EACH PLAYER. THERE WERE NO DIFFERENCES BETWEEN THE GROUPS IN THE INTENSITY OF SHOCK CHOSEN FOR THEMSELVES AND FOR THE OTHER PLAYERS. THE PSYCHOPATHS GAVE SMALL UNCONDITIONED SKIN CONDUCTANCE RESPONSES TO SHOCK DIRECTLY RECEIVED AND TO SHOCKS DELIVERED TO THE OTHER GROUP. THERE WERE NO DIFFERENCES BETWEEN GROUPS IN THE UNCONDITIONED HEART RATE RESPONSE TO EITHER DIRECT SHOCK OR TO SHOCKS DELIVERED TO THE OTHER GROUP. THE PSYCHOPATHS EVIDENCED SMALL ELECTRODERMAL ORIENTING RESPONSES AND ANTICIPATORY RESPONSES TO THE TONES PRECEDING SHOCK TO SELF AND TO OTHERS. THE NONPSYCHOPATHS GAVE RELATIVELY LARGE ORIENTING RESPONSES AND ANTICIPATORY RESPONSES TO THE TONE AND SMALL ONES PRIOR TO THE SHOCKS TO THE OTHER GROUP. BOTH GROUPS GAVE A BIPHASIC CONDITIONED HEART RATE RESPONSE--ACCELERATION FOLLOWED BY DECELERATION. THE ELECTRODERMAL DATA WERE CONSISTENT WITH THE VIEW THAT PSYCHOPATHS EXPERIENCE LITTLE FEAR AROUSAL PRIOR TO RECEPTION OF AVERSIVE STIMULI BY THEMSELVES OR BY OTHERS. IT IS SUGGESTED THAT THE ANTICIPATORY HEART-RATE RESPONSES OF THE PSYCHOPATHS WERE PART OF AN ADAPTIVE RESPONSE THAT HELPS THEM COPE WITH STRESS. TABULAR DATA AND REFERENCES ARE PROVIDED. (AUTHOR ABSTRACT MODIFIED--DAG)