A new low-dosage form of norethynodrel with mestranol (Enovid E), containing 2.5 mg of the progestational agent and 0.1 mg of mestranol, was studied in 3,510 menstrual cycles among 259 women with the minimum of a high school education. The medication was 100% effective as a contraceptive and was medically accepted among 91% of the patients. Simplified dosage schedules and methods of managing side effects were developed. Biopsies revealed that the endometrium of patients receiving the drug continued to respond to hormonal stimulation after two years, without pathological changes. The appearance of the endometrium was consistent and predictable at various stages of the menstrual cycle; it was characterized by secretory regression.