Treatment of diffuse cutaneous leishmaniasis (DCL) caused by Leishmania aethiopica remains unsatisfactory as the parasite is relatively insensitive to antimonial compounds. Reports of the clinical effectiveness of aminosidine sulphate, especially in combination with sodium stibogluconate, in visceral leishmaniasis and the finding that this antibiotic is potent against L. aethiopica in vitro, prompted us to evaluate its usefulness in DCL. Two patients with long-standing, active DCL were treated for 60 d with aminosidine sulphate, 14 mg/kg/d parenterally. The skin lesions resolved completely in both patients although they relapsed subsequently. Synergism between aminosidine and stibogluconate was demonstrated in vitro against parasites isolated from the patients. This led us to administer combined therapy, aminosidine sulphate 14 mg/kg/d and sodium stibogluconate 10 mg/kg/d, to the 2 patients in relapse and to another, third patient. Treatment was continued for 2 months beyond parasitological cure. Side effects were minimal. Following treatment, a return of specific cell-mediated immunity occurred, as expressed by a moderate infiltration of lymphocytes into the lesions and by lymphocyte proliferation in vitro in the presence of live Leishmania antigen, with synthesis of interleukin-2 and interferon gamma with one patient and interleukin 4 with the other. During follow-up periods of 2 to 21 months after treatment, no sign of relapse was seen.