It has been established that progesterone will induce 17 beta-estradiol (E2) dehydrogenase in the human endometrium. Whether it plays a similar role in the induction of estrogen sulfotransferase is not known, although this is likely, since estrone sulfate is the main metabolite of E2 when incubated with secretory, but not proliferative, human endometrium. We have now examined the influence of progesterone on both enzymes in endometrial tissue in organ culture. Estrogen sulfotransferase activity was not detectable in the cytosol of proliferative tissue when cultured in the absence of hormone, but was induced by culture in the presence of progesterone to a value (mean +/- SEM) of 19.7 +/- 5.3 pmol E2-3-sulfate h-1 mg cytosol protein-1. A significant (P less than 0.05) induction of E2 dehydrogenase activity was also observed in the same tissues [from 3.7 +/- 1.9 to 10.4 +/- 2.7 (mean +/- SEM) nmol estrone h-1 mg microsomal protein-1]. Corresponding values for secretory endometrium, when cultured under identical conditions in the absence of progesterone, were 20.3 +/- 11.6 pmole h-1 mg-1 and 31.1 +/- 25.1 nmol h-1 mg-1 for estrogen sulfotransferase and E2 dehydrogenase, respectively. Values not significantly different from these were obtained when progesterone was present in the cultures. These data indicate that progesterone secretion during the luteal phase is responsible for the induction of both E2 dehydrogenase and sulfotransferase activities in the endometrium. It is likely that these enzymes are closely coupled, resulting in the rapid metabolism of E2 by formation and excretion of estrone sulfate.