Biopsy specimens from the chest, palm, back, and lateral calf were obtained from three patas (4-6 kg) and two rhesus monkeys (6 and 8 kg) tranquilized with ketamine hydrochloride (10 mg/kg). The eccrine sweat glands of the specimens were subsequently isolated under a stereomicroscope and prepared for analysis. In both palmar and hairy skin (chest, lateral calf) patas eccrine glands were larger than those isolated from corresponding sites obtained from the rhesus specimens. In vitro stimulation of the patas' glands with methacholine (MCH) chloride produced a dose-dependent increase in sweating rate that was blocked by atropine. Maximal palmar sweating was comparable between the two species of monkey. Mean maximal in vitro sweating rates on the chest and lateral calf of the three patas monkeys were 3.79 and 4.6 nl. gl-1.min-1, respectively. In contrast, the in vitro sweating rate of the rhesus chest glands was negligibly small, i.e., 0.05 nl.gl-1. min-1. Maximal in vivo sweating rates measured by resistance hygrometry during exercise in a hot (40 degrees C) environment were usually synchronous, cyclic, and only slightly below maximal in vitro rates. When the monkey (patas) was already sweating, the onset and cessation of exercise produced an immediate rise and decline in sweating, respectively. At any given rectal or mean skin temperature, sweating was two- to sixfold higher in the patas compared with that of the rhesus monkey. These results indicate that the patas monkey is an excellent model for studying the physiology of sweating in humans.