For the first time, in the Amazon region, a mixed infection of two Leishmania was found in a patient suffering from dermal leishmaniasis. L. mexicana amazonensis was isolated from one lesion and L. braziliensis braziliensis from another. Both parasites were characterized in sandflies, hamsters, in vitro cultures, by their morphology and by isoenzyme studies in starch gel. The Authors conclude that the occurrence of this case combined with the known lack of cross immunity between most leishmanial parasites means that a vaccine for this region must be polyvalent.