In a double-blind randomized study, 92 patients with culturally proven tinea corporis and/or tinea cruris were treated orally with either terbinafine (Lamisil) (125 mg b.i.d.) or griseofulvin (500 mg b.i.d.) for up to 6 weeks. The two groups of patients and distribution of the target lesions were similar, but the analysis of the clinical scores showed that the terbinafine group had slightly higher mean scores at baseline (P = 0.186). At the end of therapy the proportion of patients with negative microscopy and culture was 78% in the terbinafine group and 83% in the griseofulvin-treated group. At the assessment 8 weeks after the end of therapy the percentages of terbinafine- and griseofulvin-treated patients with negative mycology were 93 and 95%, respectively. There were three relapses after mycological cure in the griseofulvin group (8%) and two in the terbinafine group (4%). Griseofulvin-treated patients were treated for shorter periods than terbinafine-treated patients (i.e. 58% compared to 26% received only 2-4 weeks of therapy). In terms of overall effectiveness, there were no significant differences between the two treatments. Thirty-seven terbinafine patients (77%) compared to 36 griseofulvin patients (82%) had overall effective therapy. Eight terbinafine patients (16%) compared to 10 griseofulvin patients (20%) experienced at least one adverse event. Five patients in the terbinafine group and six in the griseofulvin group had to stop the treatment due to headaches or gastrointestinal disorders. One terbinafine patient had an elevation of liver function tests after 6 weeks of treatment.(ABSTRACT TRUNCATED AT 250 WORDS)