On the basis of a review of research with animals and humans, it is argued that a broad range of aversive conditions evoke both flight and fight inclinations. Various factors determine the relative strengths of these dispositions so that the instigation to aggression is not always apparent in overt behavior. Further, it is also maintained that the aversively stimulated aggressive inclination in animals and humans is not only directed toward the diminution of the noxious stimulation, although negative reinforcement of the aggressive reaction can be an important factor in many instances. Some influences, such as classical conditioning, are common to animals and humans, but thought processes are probably more important in affecting human reactions to aversive events. The role of these thought processes is discussed, and it is suggested that Schachter's cognitive theory of emotions, with its emphasis on the self-labeling of feelings, does not apply to aversively stimulated aggression. A neoassociationistic network conception of emotions is favored as an alternative. It is also proposed that the thoughts and memories influencing the emotional experience and behavior can operate at various times in the sequence. The effect of learned helplessness is discussed in connection with this type of aggression. The thesis is also extended to the hostile tendencies often displayed by depressives, and it is suggested that the pain and suffering experienced by depressives contribute to their disposition to aggression.