Isoenzyme profiles were obtained following polyacrylamide gel electrophoresis of crude extracts of Candida albicans and C. tropicalis. The two species were separated by distinct isoenzyme patterns. Within each species, variations were found for several isoenzymes. This allowed the development of a method for biotyping these fungi. Isoenzyme patterns of the sucrose-negative variants "C. stellatoidea" and "C. paratropicalis Baker, Salkin, Pincus, and D'Amato" were obtained and subjected to cluster analysis. This procedure failed to place the variants into clusters that were clearly distinct from the conventional sucrose-positive strains. All sucrose-negative strains were found to have alpha-glucosidase activity. There was an almost complete lack of heterogeneity in the isoenzyme patterns of 11 C. stellatoidea type I strains.