Between 1981 and 1987, 486 wild mammals collected from 13 sites in French Guiana were examined for Leishmania. Eleven of 31 two-toed sloths, Choloepus didactylus, were infected, 4 of the isolates being identified as L. braziliensis guyanensis. This species was also found in 2 Didelphis marsupialis and 2 Proechimys sp. L. mexicana amazonensis was isolated from 3 Proechimys sp., 2 of which were P. cuvieri. The role of these mammals in the life cycles of the 2 anthropotropic species of Leishmania encountered in French Guiana is discussed.