The energy cost of walking (Cw) and running (Cr), and the maximal O2 consumption (VO2max) were determined in a field study on 17 Pygmies (age 24 years, SD 6; height 160 cm, SD 5; body mass 57.2 kg, SD 4.8) living in the region of Bipindi, Cameroon. The Cw varied from 112 ml.kg-1.km-1, SD 25 [velocity (v), 4 km.h-1] to 143 ml.kg-1.km-1, SD 16 (v, 7 km.h-1). Optimal walking v was 5 km.h-1. The Cr was 156 ml.kg-1.km-1, SD 14 (v, 10 km.h-1) and was constant in the 8-11 km.h-1 speed range. The VO2max was 33.7 ml.kg-1.min-1, i.e. lower than in other African populations of the same age. The Cr and Cw were lower than in taller Caucasian endurance runners. These findings, which challenge the theory of physical similarity as applied to animal locomotion, may depend either on the mechanics of locomotion which in Pygmies may be different from that observed in Caucasians, or on a greater mechanical efficiency in Pygmies than in Caucasians. The low Cr values observed enable Pygmies to reach higher running speeds than would be expected on the basis of their VO2max.