The influence of two different reinforcers of aggression was investigated: Frustration (intrinsic primary reinforcement) and instrumental value of aggression (extrinsic primary reinforcement). In the first part of the experiment frustration was manipulated on two levels by having the stooge interfere very often or seldom in the ‚building a village' task of the subject. In the second part of the study the stooge had to judge distances in traffic while the subject was allowed to give him electrical shocks in order to startle and hinder the stooge in his estimation task. The aggression score of the subject was formed by the number and the intensity of the shocks delivered. Instrumentality of aggression was manipulated on two levels by indicating or not that the subjects could earn more money the more and stronger they shocked their partner. Confirming the predictions, significantly more aggression was expressed when this could lead to earning more money than in those conditions where this was not the case. Also confirming predictions, the impact of instrumentality on aggression was stronger than the influence of frustration. Frustration did not lead to a significant increase in the level of aggression.