In the investigated Candida guilliermondii strain after growth on n-alkanes as the only carbon and energy source 5--10 nMol cytochrome P-450 per g cells (wet weight) could be detected. Cytochrome P-450 and alkane hydroxylase activity was found in the 100 000 xg pellet. Cofactor studies and inhibition experiments revealed the existence of a NADPH-dependent cytochrome P-450 alkane hydroxylase system.