Progesterone, when ingested, is only one-third to one-fifth as effective as ethisterone (17-α-ethinyl testosterone) and the latter is only one-fifth as effective as parenteral progesterone (1, 2). A new steroid, norethisterone (17-α-ethinyl-19-nortestosterone), has been shown to have an activity five times greater than that of ethisterone when administered orally to rabbits (3). The purpose of this communication is to present our data on the effectiveness of this new progestinal steroid when employed in humans.

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