The first of these two articles presents the methods, results, and discussions of six experiments which employed an avoidance of time-out from positive reinforcement schedule with human subjects to investigate: (1) whether time-outs may be considered aversive events; and (2) if so, whether the aversiveness was sufficient to produce aggressive behavior. Results showed that time-out from positive reinforcement functions as a negative reinforcer for human avoidance behavior, and also elicits aggressive behavior under certain conditions within the avoidance paradigm. Extensive research is cited both in the introduction and the general discussion. The second paper describes a similar study which sought to explore methods for the automatic measurement of aggression in humans in a situation where independent and dependent (aggressive behavior) variables were specified. Fourteen college freshmen served as subjects to determine whether the blocking of reinforcement by a rat elicited aggressive behavior toward the rat. All responses were in the form of pushing buttons. Results showed that many subjects responded to the blocking of reinforcement by the rat by inflicting pain on it. (TL)