Estradiol receptor (ER) and progesterone receptor (PR) levels were measured in 216 endometrial adenocarcinomas. Tumors containing more than 10 fmol/mg protein (for ER) and 20 fmol/mg (for PR) were considered receptor-positive. Tumors were both ER- and PR-positive in 75%. In stage I and II tumors, ER and PR levels were significantly higher than in stages III and IV. A similar relationship was established for minor (not deeper than 0.5 cm) and considerable involvement (deeper than 0.5 cm). There was an inverse correlation between ER and PR levels and ER- and PR-positive tumors incidence, on the one hand, and anaplasia, on the other. Adjuvant progestin therapy proved ineffective in tumors with a PR level under 100 mol/mg protein.