AbstractHydroxylation of progesterone at C‐6, C‐11, C‐17, C‐21 as well as formation of 11α‐hydroxyallopregnane‐3,20‐dione was successfully performed with cell homogenate of a local strain ofRhizopus nigricansREF 129. Progesterone was only transformed to 17α‐ and 21‐hydroxy derivatives with the supernatant solution of the cell homogenate.5α‐Hydrogenase,β‐hydroxylase, and 11α‐hydroxylase appeared to be located in the cell‐sediment fraction. Successful isolation of a cell preparation containing 11α‐hydroxylase system was obtained by treating the cell‐sediment fraction with citrate buffer, then by precipitation with ammonium sulphate. The formation of 6β,11α‐dihydroxyprogesterone was hindered by the addition o