The effect of REM sleep deprivation (RSD) on intraspecies aggressiveness in female Sprague-Dawley rats was investigated. Female rats were divided into 10 trial groups. Among individual groups, rats were randomly assigned to an RSD, a dry control, or a wet control condition. Each triad was given a 20-min pretreatment dominance test, and the animals were then placed into their respective conditions for 4 days. Posttreatment dominance tests were given on Day 5 immediately following treatment, Day 10, and Day 15. Contrary to the findings of some previous studies, the difference in this form of aggression between RSD and control animals was not significant. When viewed in the context of the existing studies, the present data suggest that RSD does not have a general activating effect on aggression, and that in the specific instances where positive results for intraspecies aggression have been reported, these may be the consequence of complex interactions of RSD with other variables.