The yeast Trichosporon montevideense CBS 6721 expressed large amounts of cytochrome P450 after cultivation in a glucose-peptone medium. The P450, which could be detected in the cytosolic fraction after cell breakage and ultracentrifugation, was purified to electrophoretic homogeneity and migrated in SDS-PAGE with a M(r) of 43,000. As indicated by IEF, the preparation consisted of two different P450 isoforms with pI-values of 5.9 and 6.2, which were named P450MS1 and P450MS2 respectively. Both isoforms had a characteristic maximum at 446 nm in the reduced carbon monoxide difference spectra. Partial N-terminal sequencing of P450MS1 and P450MS2 demonstrated a high degree of sequence homology between the soluble P450 enzymes of T. montevideense CBS 6721 and their close relationship to the soluble P450 forms of Trichosporon spec. SBUG 752, T. cutaneum ATCC 58094 and to the P450s of the CYP55 family of Fusarium oxysporum and Cylindrocarpon tonkinense.