Forty-eight subjects, half of whom were assigned to a condition of massive retaliation (MR) and half of whom were not (NMR), competed against a presumed opponent The loser on each trial received a shock of intensity level selected by the winner at the beginning of a trial and, simultaneously, feedback on the opponent's shock setting The winner received only feedback on the opponent's shock setting Defeat and feedback of aggressive intent (opponent's shock setting) were varied independently In the MR condition, an extreme level of shock could be selected Although its use was avoided, its psychological presence influenced perception of the opponent, aggressive behavior, and physiological arousal Consistent with previous findings, primary frustration was found to be a relatively inconsequential instigator to aggression compared to learned social attitudes