The gestagenic activity of new 17alpha-hydroxyprogesterone analogs was studied in experiments on infantile female rabbits (Clauberg-McPhail assay) and ovariectomized animals (Comer-Allen assay). The new steroidal preparations produced significant secretory transformations in immature rabbit endometrium. The maximum gestagenic activity was observed for butagest, while the minimum effect was produced by duhydrogesterone (dufaston). Butagest, megestrol capronate, and AMOL isopropyl ester showed the ability to maintain pregnancy in ovariectomized female rabbits. The compositions of gestagens (0.8 mg/kg) with ethinylestradiol (0.04 mg/kg) produced high contraceptive effect in rats.