The flow cytofluorometric susceptibility test (FCST) was extended from Candida albicans to additional clinically relevant yeasts. Candida tropicalis, C. parapsilosis, C. lusitaniae, C. krusei, C. guilliermondii, Torulopsis glabrata,and Rhodotorula rubra were also amenable to the FCST. Of the most frequently encountered yeasts, C. albicans and C. tropicalis exhibited the E(max) response, which is believed to be an in vitro indicator of ketoconazole susceptibility with potential clinical relevance. Torulopsis glabrata, for which ketoconazole therapy is less effective, did not exhibit the E(max) response; rather it exhibited an MIC effect, but usually at ketoconazole concentrations greater than those therapeutically achievable.