Leishmaniasis remains endemic in China, especially in the west and northwest frontier regions in central Asia. Epidemic outbreaks of both visceral and cutaneous forms of the disease have become a serious concern in view of such events occurring in neighboring countries. In the present study, we have begun to characterize available parasites as an initial step in understanding the epidemiology of leishmaniasis in central Asia. Nineteen Leishmania isolates collected since the 1950s from epidemiologically different foci in China were separated into five genotypes (Groups I-V) based on their polymorphisms in both kinetoplast (kDNA) and nuclear (nDNA) DNAs. Both kDNA and nDNA are conserved in Group I, which consists of six isolates, i.e., five cases of human kala-azar and one case of canine leishmaniasis isolated from three distant foci more than 30 years apart. In contrast, both kDNA and nDNA are heterogeneous in Group II, consisting of 10 isolates scattered in the plain area from the eastern coast to the western desert. This group includes five kala-azar cases, one post-kala-azar dermal leishmaniasis case, two sand fly isolates, and two canine isolates. The remaining three groups (III-V), two from great gerbils (Rhombomys opimus) and one from a kala-azar case, differ among themselves and from the aforementioned groups. Groups I, II/III, IV, and V contain isolates that have been recognized epidemiologically or typed isoenzymatically as L. donovani s.l., L. infantum s.l., L. turinica, and L. gerbilli, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)