The Leishmania donovani complex, which consists of L. donovani, L. infantum-L. chagasi, and L. archibaldi, is responsible for visceral manifestations of leishmaniasis. Multilocus enzyme electrophoresis is the standard method for the characterization and identification of strains of Leishmania. For L. infantum, the predominance of zymodeme MON-1 significantly reduces the discriminative power of this approach. In the present study, we developed 17 independent polymorphic microsatellite markers for the typing of strains of L. infantum, with the main emphasis on zymodeme MON-1. The discriminative powers of 11 markers selected from among these markers were tested by using a panel of 63 isolates of the L. donovani complex. Unique multilocus genotypes were observed for the strains analyzed, with only three exceptions. Model-based and distance-based analyses of the data set showed comparable results. It was possible to discriminate between L. donovani sensu stricto, a non-MON-1 group of L. infantum isolates, and a MON-1 group of L. infantum isolates. Within MON-1, three clusters with geographical correlations became apparent. The frequency of heterozygosity in the alleles analyzed varied extremely between the different groups of isolates. The main clusters described are not consistent with species definitions based on isoenzyme analysis but confirm the results of former PCR-based investigations.Leishmania is a genus of protozoan flagellates that cause a broad spectrum of diseases, ranging from self-limiting localized cutaneous lesions to visceral leishmaniasis with fatal spontaneous evolution (2). The majority of visceral manifestations are caused by parasites of the Leishmania donovani complex (26), which consists of L. donovani Ross, 1903; L. infantum Nicolle, 1908-L. chagasi Cunha and Chagas, 1937; and L. archibaldi Castellani and Chalmers, 1919. Currently, multilocus enzyme electrophoresis (MLEE) is the generally accepted "gold standard" for the identification and classification of isolates of Leishmania. By this method, strains are divided into groups with identical enzyme patterns, called "zymodemes." The main criticism of this approach is that genotypes are assayed indirectly, with the consequence that nucleotide substitutions may not be observed in synonymous sites or in nonsynonymous sites, if it is assumed that subsequent changes in the amino acid composition do not lead to different electrophoretic mobilities. In contrast, posttranslational modifications may change the electrophoretic mobilities, despite identical genotypes. Furthermore, the method is quite slow, laborious, and costly. Growth in vitro is inevitable, and the data sets of the few laboratories in which these analyses are performed are difficult to compare.Unlike, e.g., L. donovani or L. tropica, which present extended genetic and enzymatic polymorphisms (27, 53), L. infantum is a relatively uniform species (46). More than 80% of the strains of L. infantum isolated thus far belong to the predominant zymodeme, 42). The alternative methods for ...