Aerobic power tests were carried out on twenty male Bushnegroes, as part of a medical survey in two villages on the Upper Marowijn river in the interior of Surinam (South America). The subjects were submitted to a discontinuous series of increasing submaximal loads by means of a bicycle ergometer. Heart rate and oxygen uptake were measured at each load. The maximum oxygen uptake was estimated according to Lange Andersen et al. (1971) and used as an index for the physical working capacity. The mean aerobic power of the Bushnegroes was 35 ml O2/min/kg body weight or 2.2 l l O2/min per individual. These values are low in comparison with results obtained from professional forest workers in Surinam or in other countries.