Third-party-instigated aggression was examined by manipulating the provocativeness of the same or a new target in Part 2 of a task. Effects of previous experience with aggression (i.e., interacting with partners supportive of or disapproving of aggression in Part 1) were also examined. Although the provocativeness of the target accounted for the most variance in the amount of aggression expressed, when the target in Part 2 was new, prior experience influenced aggression. Results are discussed in terms of and interactional model of behavior. The clearer the current situational demands (i.e., known, predictable target) were, the less the influence of past aggressive experience on continued aggression; the more ambiguous the current situation (i.e., new, unpredictable target) was, the more the influence of past aggressive experience on continued aggression.