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Seborrheic dermatitis and its minimal variant, dandruff (pityriasis simplex capillitii), are among the most frequent diseases caused by Malassezia (M.) yeasts. Treatment studies have shown that antimycotics achieve clinical improvement, while recolonization leads to recurrent symptoms. Among the antimycotics used are azoles, hydroxypyridones, and various agents such as zinc pyrithione, tar, and selenium disulfide. However, comparative efficacy studies in vitro should not only consider the minimal inhibitory concentrations against Malassezia yeasts but also the bioavailability of the individual substances with regard to hair and scalp. By means of a new method, the hair strand test, hairs from ten volunteers were subjected to standardized 5-min incubation with different shampoo formulations. Thereafter they were rinsed with running water for 1 min and dried. Two hundred each of these hairs (length 1 cm) were given into a medium (olive oil on selective agar for pathogenic fungi) inoculated with M. sympodialis or M. globosa (5 x 10(3) CFU/microl), and the influence on growth was semiquantitatively determined over a period of up to 18 days. According to preliminary results, 1% climbazole proved to be particularly effective. The hair strand test, which can also be performed ex vivo, is a new method to find out whether antimycotic agents bind differently to the hair substance and, via a depot effect, may influence the growth of Malassezia yeasts and thus affect dandruff. This allows conclusions about the efficacy of antidandruff formulations.