Long-chain sphingoid bases, e.g. phytosphingosine, sphingosine and sphinganine, main constituents of the stratum corneum, can strongly inhibit the growth of microorganisms that are known to have undesirable effects on the skin. The aim of this study was to investigate the in vitro activity of different phytosphingosine preparations against Malassezia furfur, and, in comparison, against the common facultative pathogenic yeast Candida albicans. An agar dilution test for minimum inhibitory concentration (MIC) investigation of phytosphingosine base, phytosphingosine lactic acid salt, phytosphingosine HCl, and phytosphingosine glycolic acid salt was carried out using D.S.T. agar containing 2% olive oil and 0.2% Tween 80, to allow growth of the lipophilic yeast. M. furfur growth inhibition in vitro could be achieved only at extremely high phytosphingosine concentrations. Phytospingosine base had the lowest MIC value (mean 6,250 microg/ml, corresponding to 0.63% of phytospingosine in the agar). For the different phytosphingosine salts--lactic acid salt, HCl and glycolic acid salt--4-8 fold higher MIC values were noted. Unexpectedly, there was a growth stimulating effect of Malassezia at lower phytosphingosine concentrations. In comparison, growth of Candida albicans strains was inhibited at phytosphingosine concentrations between 152 and 269 microg/ml.