A total of 231 isolates of Candida species including 163 of Candida albicans (132 of serotype A and 31 of serotype B), 42 of Candida tropicalis, 17 of Candida glabrata, 7 of Candida parapsilosis and 2 of Candida krusei were collected from clinical specimens in two medical centers, one in Japan and the other in the United States. The in vitro antifungal activities of amphotericin B, 5-fluorocytosine, miconazole and fluconazole were evaluated for the above isolates by means of a photo-read broth microdilution method for determination of the 30% inhibitory concentration (IC30). The results showed that IC30 values of fluconazole were generally great compared with those of the other drugs, regardless of Candida species. The isolates of C. albicans serotype B showed a significantly lessened susceptibility to 5-fluorocytosine compared with those of serotype A (p less than 0.01). This method has the advantage of objective measurement, thus minimizing observer variability as compared with the agar dilution test.