In a double-blind clinical study 90 women with vaginal candidosis were randomly assigned to treatment with either single-dose ketoconazole (400 mg or 800 mg) or placebo vaginal suppositories. Microscope checks of vaginal fluid and mycological cultures were performed one week and four weeks after the treatment. The four weeks observation period gave no evidence for any significant differences among the three groups regarding symptoms reported as well as clinical picture and microscopy findings. Cure rate after one week, as determined by fungal cultures, was significantly lower in the placebo group (43%) than in the 400 mg (60%) and 800 mg groups (76%; p = 0.031). The mycological cure rate after four weeks did no longer show a significant difference between the groups tested, being 47% in the placebo group and 67% in each of the ketoconazole groups. Treatment of the sexual partner as well as predisposing factors did not influence the therapeutic effect. Due to the low ketoconazole serum concentrations after absorption of single vaginal doses, topical ketoconazole treatment can be applied in pregnancy. It remains to be tested, however, whether repeated vaginal application over three to five days will render higher and longer-lasting cure rates.