The aim of this study was to ascertain the inhibitory effect of several progesterone derivatives for 5α-reductase types 1 and 2 isozymes and to determine the binding to the androgen receptor. The 3, 20-dioxopregna-4-ene-17α-yl acetate 4 containing an acetoxy group in C-17 and steroid 17α-hydroxypregn-4-ene-3, 20-dione 5 having a hydroxyl group in the same position inhibited both isozymes. On the other hand, 17α-hydroxy-4, 5- ...