The pattern of oxygen consumption () for Lemur fulvus deviated from the Scholander-Irving model of energetics. Minimal rate of metabolism was 0.139 cm2 O2 g−1 h−1, which is 28% of the basal value expected from the Kleiber relationship for a mammal of 2.33 kg. This minimal rate occurred at ambient temperatures (Ta) from 30–40°C; thermal conductance (C) at Ta of 22–30°C was 0.235 cm2 O2 g−1 h−1 °C−1. Deviation from the standard model occurred most notably at Ta < 22°C as rate of metabolism and thermal conductance decreased. At Ta = 0–7°C, #### was 0.152 cm3 O2 g−1 h−1, and C was 0.0037 cm3 O2 g−1 h−1 °C−1, which are 31% and 18% of the expected values, respectively. Below 0°C, #### increased. A high body temperature, 38.2°C, was maintained at Ta from −2 to 40°C. The low minimal rate of metabolism of L. fulvus may be partially explained by its folivorous diet. It is also possible the minimal rate was a depressed rate, below that referred to as basal in the standard model. Low #### and C at cold Ta's probably resulted from decreased peripheral circulation and a heat conserving posture at abnormally cold environmental temperatures.