A complete, commercially available, integrated telemetry and data acquisition system is described, which is used to record core temperature and activity in mice. The system is comprised of a telemetry transmitter (implanted in the peritoneal cavity), a receiver (placed underneath the cage) connected to a computer with software (Dataquest), which converts the transmitter signals directly into core temperature and activity. The information is stored on either a floppy diskette or a hard disk in the computer. The effects of anesthesia (sodium pentobarbital, halothane), handling, aggregation, restraint, a cholinergic agonist (oxotremorine), and an anticholinesterase agent, soman (pinacolyl methylphosphonofluoridate), on core temperature and activity were examined. The telemetry system for the recording of core temperature and activity provides a more accurate assessment of the temporal effects of various drugs and is more efficient and less labor intensive than the use of a rectal temperature probe.