Bifonazole, clotrimazole, flutrimazole, ketoconazole, miconazole and sertaconazole were tested for their activity against 23 isolates of Malassezia furfur by agar dilution in vitro. Topical formulations of the same agents were evaluated for efficacy against M. furfur skin infections in guinea pigs in vivo. The most potent inhibitor in vitro was ketoconazole (geometric mean minimum inhibitory concentration 0.51 microgram ml-1), followed by bifonazole (8.1 micrograms ml-1), then miconazole (14 micrograms ml-1), clotrimazole (15 micrograms ml-1) and flutrimazole (16 micrograms ml-1), with sertaconazole the least active (52 micrograms ml-1). In animal experiments involving three consecutive days of topical treatments, bifonazole 1% cream, clotrimazole 1% cream, flutrimazole 1% and 2% creams, ketoconazole 2% cream and shampoo and miconazole 2% cream all reduced M. furfur dermatitis lesion severity below that of untreated control animals; however, sertaconazole 2% gel and cream showed no reduction in lesion severity below control. The results confirm that ketoconazole is a more potent inhibitor of M. furfur in vitro than other topical antifungal agents of its class and suggest that sertaconazole is the least effective of such agents among those tested.