PIP: 4 cases of adenocarcinoma of the endometrium were reported in young women. All were using and had used for periods of 4-12 years a sequential oral contraceptive, Oracon, manufactured by Mead Johnson Laboratories. Ethinyl estradiol and mestranol, the 3 methyl ether of ethinyl estradiol, are 25 times more potent than diethylstilbestrol, which has recently been implicated in the development of vaginal adenocarcinoma in female offspring of women treated during pregnancy with it. A study is now in progress to determine whether long-term use of Oracon produces premalignant changes in the endometrium. Doctors with patients on similar sequential contraceptives should watch for abnormal vaginal bleeding.