Eight patients from Zaire with Mycobacterium ulcerans infection were treated by the local application of heat to maintain a temperature of approximately 40 degrees C in the ulcerated area. All lesions healed without surgical intervention and without local recurrences during follow-up periods of up to 22 months. This study shows that local heat promotes healing of M. ulcerans lesions. We postulate that the mechanism is primarily by direct inhibition of multiplication of M. ulcerans. Other possible contributory effects are discussed.