Leishmaniasis, a group of visceral and cutaneous diseases, is caused by parasites belonging to one genus comprising approximately 13 different species. Many methods including serological, biochemical and molecular biological techniques have been used by various workers to characterize these different species and isolates of Leishmania, yet there is no single generally accepted criterion. We have identified certain cDNA clones from a library generated from the promastigotes of S1 strain of Leishmania donovani and used them as probes for identification of various isolates of L. donovani and Leishmania tropica. Two of the probes used, E2b (2.0 kb) and Ela (1.3 kb), sequence characterized to be hsp70 of Leishmania, were able to distinguish various isolates of L. donovani from different geographical origins as well as strains of L. donovani from those of L. tropica. Thus, by using recombinant hsp70 cDNA probes, the data indicated that there is a considerable degree of heterogeneity in the heat-shock genes of Leishmania.