Users of combined oral contraceptives may have a 50% lower risk of developing endometrial cancer than nonusers, according to a recent study which also confirms that users of sequential pills have a much greater risk of developing it. An accompanying editorial however cautions that because of the small numbers involved in the study, the apparent protective effect of the combined pill may be due to chance. The investigators identified all white women aged 35-54 in a 2-county area of Washington in whom endometrial cancer had been diagnosed between January 1975 and December 1977, and successfully interviewed 117 of them. 395 controls were also selected. Both groups were interviewed to determine their reproductive and menstrual histories and use of estrogen any time prior to the diagnosis. Women with endometrial cancer had used the combined pill less often than the controls, and the relative protection of combined preparations was reported to be greatest during use and for 1 or 2 years thereafter. Women who had used menopausal estrogens for 3 or more years after discontinuing pill use apparently were not protected. The increased risk of endometrial cancer among users of sequentials was due to 1 preparation, Oracon. Oracon contained a much greater quantity of a potent estrogen and a smaller quantity of a weak progestogen than other sequentials, and also included 2 more days of estrogen per cycle. Possible objections to studies implicating estrogen in endometrial cancer are cited.