Concentrations of cytosol estrogen (ERc) and progestin (PRc) receptors and the activities of 17 beta-hydroxysteroid dehydrogenase (17-HSD) were measured in 80 untreated and 23 danazol-treated endometriotic tissue specimens. The results were compared with those obtained from endometrium specimens prior to or following danazol or medroxyprogesterone acetate (MPA) treatment. The concentrations of ERc and PRc in the endometriotic tissue were lower than corresponding values in the endometrium. Cytosol female sex steroid receptors were always present in the normal endometrium, whereas only 70% of the endometriotic lesions were simultaneously ERc- PRc-positive (receptor concentration greater than or equal to 3 and greater than or equal to 6 fmol/mg cytosol protein respectively), 24% PRc-positive, and 6% receptor-negative. In the endometriotic tissue, the mean concentrations of PRc during the luteal phase of the cycle (90 +/- 23, SE, fmol/mg protein) were lower (p less than 0.05) than during the follicular phase (177 +/- 32 fmol/mg protein), while the ERc concentrations and 17-HSD activities did not show any cyclic variations. Danazol and MPA had similar effects on the endometrium, both inducing a decrease in concentration of the female sex steroid receptors and an increase in activity of 17-HSD during short-term treatment (one week), and a decrease in activity of the enzyme during long-term treatment (3 weeks). The effect of danazol on the endometriotic tissue differed from that found in the endometrium. Danazol did not alter the activity of 17-HSD or the concentration of PRc but tended to increase the concentration of ERc in endometriotic tissue when given for 7-30 days.(ABSTRACT TRUNCATED AT 250 WORDS)