The percutaneous penetration of the antimycotic terbinafine (Lamisil, SF86–327) has been assessed after topical application in patients with pityriasis versicolor and normal volunteer subjects. Plasma samples were analysed by high-pressure liquid chromatography (HPLC). In 10 patients with pityriasis versicolor plasma levels over a 28–day period did not exceed 24.8 ng/ml. There was no evidence of long-term accumulation in these patients. Similar results were obtained with a group of 8 normal volunteer subjects where the maximum plasma level recorded after application of 1% terbinafine cream over 8 days was 11.4 ng/ml. Significantly higher values were not recorded in normal subjects with reduced barrier function. The two main metabolites of terbinafine, carboxybutyl and demethyl carboxybutyl terbinafine, were also measured by HPLC in the urine of the normal volunteer subjects. There was no evidence of long-term accumulation of the terbinafine or its metabolites in these subjects.