The experimental data on the pharmacological activity of the modified analogs++ of 17 alpha-hydroxyprogesterone are presented. A high gestagenic activity was shown to be related to the presence of the methyl group in position 6, the double bond in position C6-C7, the hydroxyl and acetoxy groups in position 3. Such modification of the molecule provides a high degree of the secretory degeneration of the female rabbit endometrium at any method of administration as compared with progesterone but not always provides a high level of pregnancy preservation. Among the studied compounds, mepregenol diacetate with the acetoxy++ groups in positions 3 and 17 alpha is the most active in the ability of the secretory degeneration of the endometrium. The compound served as the basis for the development of the drug acetomepregenol possessing contraceptive and therapeutic effects.