Voriconazole was compared with amphotericin B and itraconazole by a modification of the NCCLS microdilution reference method for yeasts against 62 clinical isolates of Aspergillus fumigatus. MICs of voriconazole were slightly lower than those of amphotericin B and itraconazole. The MIC of voriconazole at which 90% of isolates were inhibited was 1 mg/L and the MIC range was 0.25-2 mg/L. Voriconazole is a new antifungal agent with potential for use in the treatment of A. fumigatus infections.