Steroidic 5.alpha.-reductase inhibitors

A compound of the following formula (I) ##STR63## wherein R.sub.1 is

• (a) hydrogen;
• (b) C.sub.1 -C.sub.6 alkyl unsubstituted or substituted by a substituent chosen from carboxy, halogen and amino;
• (c) a phenyl, .alpha.-naphthyl, .beta.-naphthyl or benzyl group, either unsubstituted or ring substituted by a substituent chosen from C.sub.1 -C.sub.6 alkyl, halogen, nitro, amino and hydroxy, or
• (d) --OR.sub.2 wherein R.sub.2 either has one of the meanings (a), (b) and (c) reported above for R.sub.1 ;
• or is a C.sub.2 -C.sub.12 -aliphatic or aromatic carboxylic acyl or a hydroxy protecting group chosen from the group consisting of dimethyltert butyl silyl, trimethylsilyl, and 2-tetrahydropyranyl;
• X is direct bond or a straight or branched C.sub.1 -C.sub.6 -aliphatic hydrocarbon chain;
• the symbol .dbd.Y represents ##STR64## or .dbd.O;
• Z is
• (a') hydroxy;
• (b') C.sub.1 -C.sub.6 alkoxy;
• or
• (c') ##STR65## wherein each of R.sub.3 and R.sub.4 is, independently, hydrogen or C.sub.1 -C.sub.6 alkyl;
• or R.sub.3 and R.sub.4 taken together with the nitrogen atom to which they are linked, from a hexatomic heteromonocyclic ring chosen from piperidino, piperazino, morpholino and thiomorpholino;
• the symbol ------ represents a single or double bond, and the pharmaceutically acceptable salts thereof.