A three-dimensional thermoregulatory model of a squirrel monkey, whose shape is approximated by 742 rectangular blocks of varying sizes, has been developed. The inhomogeneous model has four layers: a core, a composite layer of muscle and fat, skin, and fur. The model simulates the flow of heat into and out of the body, including internal heat generation (metabolism) by the body, cooling and distribution of heat by blood, thermal conduction throughout the body, evaporative heat loss from sweating, and radiation and convection from the outer surface of the body. It also simulates dynamic thermoregulatory behavior such as peripheral vasomotor responses (skin vasodilation and vasoconstriction) and variable sweating rates. Computed results are compared with available experimental data; the agreement is good, especially for ambient temperatures above 26 C.