Bovine cytochrome P450c17 monooxygenase was produced in a 30-L fermenter by Saccharomyces cerevisiae GRF18 (YEp-Toku1), harboring the GAL10 promoter, and using conditions of medium cell density culture. Upon addition of D-galactose as an inducer and FeCl3 as a cofactor, cells began to produce the P450 hemoprotein. The yield of this enzyme reached a maximum after 31 h but its formation continued for more than 60 h after induction. The amount of P450c17 produced was 4.7-fold as compared to shake flask experiments.