Apart from pityriasis versicolor, Malassezia furfur is thought to play a significant role in the pathogenesis of seborrhoic eczema and Malassezia folliculitis. However, it has not been clarified whether in addition to host factors (e.g. immune status, greasy skin), yeast-dependent activities are responsible for manifestation of the disease. In this context interstrain variability of hydrolase activity of Malassezia isolates might be significant. For determination of hydrolase activity, washed yeast suspension was applied to selective agar for pathogenic fungi containing 8% (v/v) Tween 80 or Tween 60 and was incubated at 37 degrees C for 10 days. Growth was accompanied by formation of a dense white zone around the colony, in which free fatty acids corresponding to Tween 80 (C18:1) or Tween 60 (16:0, 18:0) were demonstrated by means of thin layer and gas chromatography. Thus, this phenomenon is a parameter for yeast-dependent hydrolysis of Tween 80 and Tween 60. Considering different growth behaviour, a "hydrolase zone' (H2) was determined using the quotient colony diameter/(ring+colony) diameter in each of the 150 strains tested. Although no significant H2 variations were observed in strains of different clinical origin, the present study revealed that in addition to a known enzyme, which is located within the cell wall and/or membrane systems, these Malassezia isolates produce a very active hydrolase diffusing into the medium.