We have developed a simple in vitro method of infecting a continuous human macrophage cell line (U937) with promastigotes of several species of Leishmania. These include L. braziliensis braziliensis, L. b. panamensis, L. donovani, L. mexicana mexicana, L. m. pifanoi, L. tropica, and L. major. The growth kinetics of these species are presented as well as drug sensitivity data. The U937 cell system can be used to determine drug efficacy and eliminates the need to use amastigotes from animal tissues to infect the tissue culture.