Leishmania sp. was isolated from the livers and spleens of 4 of 56 Mastomys natalensis and one of 21 Tatera gambiana in Keana District, Nigeria; none of the rodents had cutaneous lesions. Parasites were not found in 42 Rattus rattus. Experimentally infected mice developed cutaneous lesions characteristic of L. major infection. The organisms could not be cultivated in vitro.