Avoidance behavior in single and paired rats was established by placing the animals into a chamber and allowing their shock-induced random movements to produce a bar press. Single subjects consistently performed better in the avoidance situation than paired subjects. This finding was related to the high incidence of shock elicited fighting which was observed between the paired animals. Both avoidance and fighting responses were typically made by one of the paired subjects while the other showed only the stereotyped fighting reaction. The addition of a naive subject into the chamber with a subject that had previously learned to avoid, also produced fighting behavior which disrupted the avoidance responding.