The antibacterial and antimycotic activity of econazole base, an imidazole derivative, was examined in vitro and in experimental infections of mice. Comparative minimal inhibitory concentration (MIC) determinations indicate econazole as well as miconazole to be of moderate activity against gram-positive bacteria (MICs: 0.78–25 μg/ml) and yeasts (MICs: 1.56–25 μg/ml). Against filamentous fungi, econazole exhibits better in vitro activity than miconazole and – with the exception of Rhizopus oryzae and Absidia corymbifera – MICs are markedly lower than against yeasts. No effect of nutrient media and no effect of the inoculum were observed with the four drugs. A strong influence of bovine serum on MIC values, however, suggested a strong protein binding. In experimental candidiasis of mice, no therapeutic effect with econazole base administered orally or intraperitoneally could be observed (ED50 200mg/kg). In experimental aspergillosis of mice, a slight effect, as demonstrated by the ‘minimum life-prolonging dose’ of 100 mg/kg, was found. The in vitro and in vivo results are discussed in the light of the available pharmacokinetic and toxicological data. It is concluded that more studies, especially on the pharmacology of econazole and about the clinical efficacy, are needed to come to a d