Ten replicates of two pigs each were used to determine the effects of 10 IU/kg i.m. adrenocorticotropin hormone (ACTH) or physiological saline on aggressive and submissive behaviors. Behavior was recorded for 90 minutes after pigs of each treatment were grouped. Both duration and latency to attack were similar for ACTH- and salinetreated pigs. Submissive behavior was greater for ACTH-treated pigs (P<.01). In this species, ACTH increased submissive behavior which resulted in domination of ACTH-treated pigs by control pigs.