The paper is devoted to an experimental study of the hormonal properties of two new derivatives of 17 alpha-oxyprogesterone--mepregenol monoacetate and mepregenol diacetate--for their possible use as minipills. Both compounds showed a high progestational activity which was much higher than that of progesterone and the activity of alpha-norgestrel in peroral administration. The above compounds made no inhibitory effect on hypophyseal gonadotropic function; on the contrary, they stimulated follitropine secretion. Besides, different dose-related influence of the steroids on a progesterone level was revealed: the use of small doses resulted in enhanced secretion and larger doses brought about the suppression of secretion. Thus, the new compounds of the progesterone series--mepregenol monoacetate and mepregenol diacetate--appear promising compounds for monohormonal contraception and for the management of conditions with lowered function of the corpus luteum.