Leishmania donovani organisms isolated from 10 children coming from different districts in Iraq, were compared between themselves, with Leishmania donovani isolated in Iran and the Sudan, and with a Leishmania sp. isolated from the viscera of a rat caught in Baghdad. The comparison was made by examination of the electrophoretic mobilities of seven soluble enzymes: malic enzyme E.C.1.1.1.40; glucose phosphate isomerase E.C.5.3.1.9; glucose-6-phosphate dehydrogenase E.C.1.1.1.49; phosphoglucomutase E.C.2.7.5.1.; malate dehydrogenase E.C.1.1.1.37; aspartate aminotransferase E.C.2.6.1.1 and alanine aminotransferase E.C.2.6.1.2 following thin-layer starch-gel electrophoresis. The Iraqi isolations of L. donovani fell clearly into three groups. Group A contained the organisms from seven children, six from the Wasit district and one from the outskirts of Baghdad; Group B, the organism from one child from the Hilla district (100 km south of Baghdad) with severe visceral leishmaniasis which relapsed following chemotherapy; Group C, the organisms from two children from Suaira in the Wasit district. The Iranian and Sudanese isolations gave patterns different from each other and from those from Iran. The Leishmania sp. isolated from the viscera of the rat gave a pattern identical to that of L. tropica.