Terbinafine (Lamisil) is the first safe and effective orally active agent in a new family of antifungal drugs, the allylamines. The drug has a unique site of action on sterol synthesis due to its inhibition of squalene epoxidase. The drug is highly effective against dermatophytes in vitro, and in placebo controlled trials, it is effective both topically and orally against dermatophytes. In the study reported here, terbinafine has been compared to griseofulvin in patients with moccasin type tinea pedis. Terbinafine was given at 125 mg b.i.d. and griseofulvin was given at 250 mg (microsize) b.i.d. Thirty-six patients were enrolled in a randomized, double-blind study. Patients were evaluated weekly by mycological culture, microscopy and clinical signs and symptoms for 6 weeks during therapy and at follow-up 2 weeks later. Twenty-eight of the 36 patients were evaluable for drug efficacy. Twelve out of sixteen (75%) of the terbinafine group were mycologically and clinically cured by the end of therapy (6 weeks) and 14/16 (88%) were cured at the time of follow-up 2 weeks later. Two patients were mycologically cured, but moderate signs or symptoms were present at follow-up. In the griseofulvin-treated group 3/12 (27%) were cured at the end of treatment and 5/11 (45%) at follow-up evaluation. Follow-up after 6-15 months showed continued resolution of the terbinafine-treated patients, but relapse of infection in griseofulvin-treated patients. There were two side-effects during terbinafine treatment (one gastro-intestinal, one skin allergy), and no significant changes in haematological, hepatic enzyme or renal blood tests done weekly.(ABSTRACT TRUNCATED AT 250 WORDS)