Two species of sand flies were collected by various methods from sites in the Dominican Republic. Lutzomyia cayennensis hispaniolae was the more common of the two. It was found in wooded habitats from sea level to an elevation of 442 m. This species was observed feeding on lizards (Anolis sp.) in the wild. In the laboratory, it fed only on lizards and only under lighted conditions. The other species, Lu. christophei was only found in the vicinity of seven leishmaniasis case sites. It readily fed on or probed rodents and humans. Although no naturally infected sand flies were collected, in the laboratory Lu. christophei was readily capable of transmitting the Dominican Leishmania parasite to uninfected BALB/c mice. We collected 167 specimens of three species of rodents and three Herpestes auropunctatus (mongoose) from the vicinity of two case sites. All four species are non-endemics introduced in post-Columbian times. Although we were unable to isolate parasites from any of these specimens, four of 44 Rattus rattus from one case site were seropositive for antibodies against Leishmania by indirect fluorescent antibody testing. This represents the first report of transmission of the Dominican Leishmania parasite by a sympatric species of sand fly and suggests that commensal rodents may play a role in the epidemiologic cycle.