Studies were carried out with the current leading antimycotic agents, using identical test methods, to compare their activity in vitro and in animal in vivo experiments. In the broth dilution test, the minimum inhibitory concentrations against approximately 50 strains of the most important species of yeasts, dermatophytes and moulds were determined using different culture media. Efficacy against yeasts was examined in experimentally-induced candidosis in mice treated orally, and against dermatophytes in experimentally-induced trichophytia in guinea pigs receiving topical treatment. The results showed that the imidazole derivatives studied can be regarded as true broad-spectrum antimycotics, and clotrimazole, in particular, had a well-balanced overall effect. The significance of the experimental data with respect to therapeutic efficacy in man in various indications is discussed.