There are reasons to consider incomplete the description of sleep in many non-human primate species. Recording animals by highly sensitive videos to obtain detailed descriptions of nighttime behavior and evidence of muscle activity while in a resting posture, seems a promising approach to the non-invasive study of sleep in non-human primates. The present work describes the use of ultrasensitive videocameras to record and analyze spontaneous nighttime behaviors in captive non-human primates. Its main purpose is to emphasize the utility of videorecordings to analyze nighttime behavior. A heterosexual group of nine stumptail macaques (M. arctoides) was studied. It was possible to identify resting postures: immobility or lying on the floor as well as sleep movements and behavioral signs of sleep. This procedure permits recognition of each animal individually and the data suggest that videorecordings, among other techniques available, may be a useful, non-invasive method to study sleep. © 1995 Wiley-Liss, Inc.