R41,400 is a recently synthesized, water-soluble imidazole. Its antifungal properties were compared in vitro with those of miconazole using an agar dilution procedure and 175 isolates of human fungal pathogens. The filamentous forms of Histoplasma capsulatum and Blastomyces dermatitidis were inhibited by less than or equal to 2 microgram of either drug/ml; Coccidioides immitis was inhibited by less than or equal to 0.5 microgram of R41,400/ml. Among the yeasts tested, Cryptococcus neoformans and Candida parapsilosis were the most susceptibel to the two drugs, whereas Candida albicans and Candida tropicalis were the least susceptible; 0.5 microgram of either drug/ml was inhibitory for 90%-100% of tested isolates of C. neoformans but for only less than or equal to 20% of isolates of C. albicans, C. tropicalis, and Torulopsis glabrata. Both drugs were inhibitory for most isolates of Trichophyton and Microsporum species at concentrations of less than or equal to 4 microgram/ml; Epidermophyton floccosum was uniquely susceptible to both drugs.