The in vitro activities of miconazole and miconazole nitrate against a variety of pathogenic and saprophytic fungi were studied using an agar dilution procedure. Histoplasma capsulatum and Blastomyces dermatitidis were the most susceptible of the organisms tested with inhibition of 11 isolates by 0.5μg/ml or less of either compound. Coccidioides immitis was somewhat more resistant requiring 1 or 2 μg/ml for inhibition; Sporothrix schenckii was less susceptible with 5 isolates requir ing 2 to 8 μg/ml for complete inhibition. Twelve strains of Cryptococcus neoformans were susceptible to 1 μg/ml or less. Most strains of Candida albicans were resistant to less than 16 μg/ml; other species of Candida were inhibited by from 1 μg/ml to 16 μg/ml. Of 15 dematiaceous isolates tested, all but two were inhibited by 4 μg/ml or less. Most of 15 isolates of Aspergillus were susceptible to 4 μg/ml or less. Fusarium species were highly resistant. A brief discussion of the possible clinical usefulness of miconazole is given.