Local heat treatment was tested and found effective in three patients with diffuse cutaneous leishmaniasis (DCL), a form of disease poorly responsive to the usual chemotherapy. A water bath that circulated water through a pad wrapped around the lesion provided a temperature of 39°C to 41°C for a cumulative time of at least 20 hours, over a period of several days. In the DCL patients beneficial effect of heat treatment was documented by pre- and post-treatment biopsies and cultures. Several other patients with ordinary cutaneous leishmaniasis did not respond to the same form of treatment. It was concluded that different strains and/or species of leishmanial parasites vary in their sensitivity to elevated temperature. While local heat treatment may be curative in certain cases of cutaneous leishmaniasis, such therapy is still experimental and should be monitored by quantitative parasitological studies to document its usefulness.