Miconazole at minimal fungitoxic concentrations inhibits ergosterol biosynthesis in sporidia of Ustilago maydis by interference with sterol C14 demethylation. The action is analogous to that of the fungicides triarimol and fenarimol. The fungicide 1-dodecylimidazole at low concentrations (0.1 to 0.25 mug/ml) inhibits sterol C14 demethylation; however, at higher concentrations (1.0 mug/ml or greater) it also inhibits 2,3-oxidosqualene cyclization and subsequent transmethylation. It is postulated that this diversity of effects of 1-dodecylimidazole results from binding of the inhibitor to sterol carrier protein(s).