Three imidazole antifungals (ketoconazole, tioconazole and miconazole) were examined for their effect on germ tube development by synchronous blastospore populations and on actively growing germ tubes of three strains of Candida albicans. After incubation in serum for 4 h the largest differences in germ tube elongation between strains were detected at concentrations (0.005 mg/l) where minimal inhibition was observed. Germ tube elongation in antifungal-containing serum diminished with increasing concentration. Maximum inhibition occurred at concentrations of 0.5 mg/l. All three antifungals inhibited the rate of hyphal elongation by the strains over a 6 h period at this concentration. Tests where germinated blastospores of strain 3281 were transferred to serum containing 0.5 mg/l of antifungal indicated that all three drugs inhibited further elongation. However, the rate of inhibition was dependent upon the length of time germination had proceeded in serum alone prior to transfer to antifungal-containing serum.