Toenail tinea is a very recalcitrant dermatosis. Griseofulvin at > or = 500 mg/day is the current medication of choice, but it is minimally successful. In a controlled open trial ultramicrosize griseofulvin (UMSG) at doses of 660 and 990 mg/day was compared with itraconazole at 100 mg/day in 109 patients. At 4-week intervals, the patients were evaluated for their clinical and mycological statuses and adverse reactions. Treatment was given for up to 18 months. Compliance was checked by tablet counting. Response (cure, partial cure, marked improvement) was analyzed by the intent-to-treat method. Cured and partially cured patients were followed up. Except for one early dropout, the toenails (mean, 6 to 7) were involved. Cure or partial cure was found in 6% (UMSG at 660 mg), 14% (UMSG at 990 mg), and 19% (itraconazole at 100 mg) of patients (P = 0.2097); marked improvement was found in 36, 44, and 39% of patients in the three treatment groups, respectively. Most patients had to be treated for 18 months. Failure was related to short medication periods (adverse drug reactions, dropout). While stable cure was not obtained with UMSG at 660 mg, the higher dose of UMSG and itraconazole gave stable cures in the other patients. Side effects of nausea, diarrhea, and headache were found in 20, 26, and 11 patients, respectively (P = 0.0028), and the numbers in whom medication had to be discontinued differed, too (P = 0.0137). While there was no major difference with glutamic-pyruvic transaminase and gamma-GT, total and low-density lipoprotein cholesterol levels declined slightly in the itraconazole group (P = 0.0357 and P = 0.0639, respectively, at 3 months). More than 70% of the patients had an average compliance of > or = 90%; four patients (two dropouts) were poor compliers. In conclusion, it appears questionable whether griseofulvin can continue to be considered the "gold standard" in the treatment of toenail tinea. At present, itraconazole at 100 mg shows better efficacy and is better tolerated.