A Rhesus monkey model has been developed that makes it possible to investigate physiological rhythms and circadian effects on performance in an integrated framework. Body temperature and animal activity are of great importance in the study of circadian rhythms. To monitor a free-ranging monkey's temperature, a telemetry system is used. Monkey activity is measured using strain-gage transducers mounted under the animal's home cage. Nonhuman primates are not always the most cooperative experimental subjects; therefore, some unique solutions are necessary to overcome these constraints.<<ETX>>