The efficacy and safety of daily doses of 200 mg of ketoconazole or 250 mg of griseofulvin (Fulvicin-P/G®, Schering, Kenilworth, N.J.) in the treatment of patients with infections due to dermatophytes are being evaluated in a three-center study. Patients with chronic dermatomycoses resistant to topical treatment or with infections that involve large areas of the body, a condition that indicates oral therapy, are being treated for a minimum of four weeks. Eleven (38%) of 29 patients treated with ketoconazole for four weeks and five (24%) of 21 patients treated with griseofulvin for the same amount of time were rated as cured. At completion of therapy (four to eight weeks), 24 (83%) of 29 patients treated with ketoconazole and six (32%) of 19 patients treated with griseofulvin were rated as cured (P = < 0.001). One (7%) of 14 patients treated with ketoconazole and four (80%) of five patients treated with griseofulvin were rated as relapsed within 28 days after completion of therapy (P = 0.006). No significant adverse effects have been reported for either treatment group. The preliminary results of this study have shown ketoconazole to be more effective than griseofulvin in the treatment of dermatomycoses.