Environmental, vaginal, and blood isolates of Candida parapsilosis were biotyped by karyotype analysis in pulsed-field gel electrophoresis. Morphotype and resistotype were also determined as was aspartyl proteinase secretion and pathogenicity in a systemic mouse infection model. Overall, the karyotype patterns consisted of 6-9 chromosome bands (> 3.0-0.6 Mb) with limited clustering, since most isolates had unique chromosome profiles. Major clusters C. parapsilosis, differing by source of isolation and in experimental pathogenicity, could be discriminated by morphoresistotyping. The morphotypes of isolates from subjects with candidemia ranged from one that caused elevated mortality in the normal mouse to those that were totally avirulent in the neutropenic animal. Among clinical isolates, secretion of aspartyl proteinase was higher in vaginitis than in candidemia isolates and did not correlate with the experimental pathogenicity. These results emphasize the biotype diversity of C. parapsilosis and have potentially important epidemiologic and pathologic implications.