A prophylactic vaccine composed of killed promastigotes of five stocks of Leishmania was tested as an immunotherapeutic agent against American cutaneous leishmaniasis (ACL). The agent was administered by deep intramuscular injection daily for 10 days, followed by a 10-day interval. Out of 62 patients so treated, 47 (76%) were considered clinically cured; 41 required 2-10 treatment courses and the other six 11-19 courses. None of the patients treated by immunotherapy displayed adverse side-effects. Immunotherapy proved to be effective in the treatment of single cutaneous lesions, multiple cutaneous lesions and in cases of mucocutaneous leishmaniasis. In comparison with chemotherapy (Glucantime), immunotherapy is less efficient and more prolonged but can be safely used when antimonials are contra-indicated or are found to be ineffective. Consideration is given to the treatment of victims of ACL living in rural areas remote from a medical centre.