The enzymatic profiles of several yeastlike organisms were studied using 19 substrates included in the API ZYM system. The isolates evaluated were: 186 Candida albicans, 19 C. stellatoidea, 4 C. tropicalis, 2 C. parapsilosis, 2 C. pseudotropicalis, 1 C. guilliermondii, 3 C. krusei, 11 Torulopsis (Candida) glabrata, 1 Cryptococcus neoformans, 2 Saccharomyces carlsbergensis, 1 Rhodotorula rubra, and 1 R. mucilaginosa. Esterase lipase (C8), leucine arylamidase, acid phosphatase, and phosphoamidase were detected in all of the isolates while trypsin and alpha-galactosidase were not found in any of the isolates using this system. The other enzymes were produced to a variable degree. The different enzymatic profiles might prove useful in the rapid differential diagnosis of genera and species of these yeastlike organisms. To this end, more extensive studies using more isolates of each species will be required, and enzymatic activity should be verified with other techniques and substrates.