Leishmania Viannia strains from 1,092 patients who acquired dermal leishmaniasis in endemic regions of Colombia were analyzed for expression of species and subgenus specific epitopes. Eight monoclonal antibodies prepared against membranes of the major species of the Viannia subgenus and previously shown to distinguish these species, recognized low molecular mass (< 45kD) membrane components. Thirteen widely but non-uniformly distributed serodemes were identified: one unique to L. panamensis, four unique to L. braziliensis and eight that were common to L. braziliensis and L. guyanensis. Thirty-seven percent of Colombian L. braziliensis strains concomitantly typed by isoenzymes were null, i.e., not recognized by the corresponding species-specific B-16 or B-18 antibodies. No Colombian L. guyanensis strains were recognized by the antibody specific for this species (B-19). In contrast, L. panamensis-specific B-4 and B11 antibodies recognized > 98% of the L. panamensis strains. Null strains of L. braziliensis and L. panamensis were more frequently isolated from mucosal leishmaniasis than strains that expressed species specific epitopes, suggesting that these strains may be more pathogenic.