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SummaryThe results presented indicate the necessity for determination of the purity of the P.G. isolated from non-pregnant urine. It has been clearly shown that the modifications reported by Venning1 do not necessarily remove all impurities from the final product. The implications of these findings, for much of the data in the literature, are clear. In the light of our results, the finding (first reported by Hamblen, et al.,2 that P.G. may be present in the absence of a secretory endometrium, particularly warrants critical reexamination.

Summary1) 6α-methyl-17α-acetoxyprogesterone is a highly active progestin based on its ability to promote a secretory endometrium and to prevent ovulation in rabbits. 2) Subcutaneously, 6α-methyl-17α-acetoxyprogesterone is 6 to 8 times and orally 60 to 75 times as active as 17α-acetoxyprogesterone in the McPhail assay. The ability of the 6-methyl compound to inhibit ovulation in rabbits is at least 20 times as great as that of progesterone subcutaneously, while 17α-acetoxyprogesterone is 7 times as active as progesterone.