An integrated system to record physiological and behavioral variables from nonhuman primates in social groups is described. The system records data simultaneously from two animals in family groups of five. It synchronizes behavioral and physiological data within 16 ms, either online or from recordings. Behavioral data are entered by trained observers online or from videotape. Recordings of physiological data are produced online as stripchart records, tape recordings on the audio channels of video cassettes, and magnetic disk files. The physiological data include two arterial blood flows, arterial blood pressure, and heart rate. The data are transmitted from freely behaving animals to a central site via radio telemetry. The infrared link controls the radio transmitter and physiological signal-processing electronics, as well as two sources of drugs for each animal. All of the electronics are contained in a small, light backpack that can be worn by either male or female baboons.