Laboratory studies have resulted in classification of the marbled African lungfish, Protopterus aethiopicus, as an obligate air-breather. However, there have been no investigations of the extent of dependence on aerial respiration by this species in the wild. We used radio telemetry to obtain quantitative information on the surfacing frequency of lungfish in Lake Baringo. The results showed radio-tagged lungfish came to the surface during the period immediately following their release but that aerial respiration later ceased, indicating that the fish were able to meet their metabolic oxygen requirements solely through aquatic respiration. These results suggest that under certain conditions lungfish in the wild may not be obligate air breathers and that the use of aerial respiration may be a function of ecological as well as physiological factors.