A report is made of a pilot study on the effect of administration of a cyclical or continuous course of a combined estrogen and progesterone preparation on bleeding patterns and the endometrium. Small treatment groups received either 1) cyclical estradiol valerate 2 mg plus norgestrel .5 mg for 21 of 28 days; 2) continuous estradiol valerate 2 mg plus norgestrel .5 mg daily; 3) continuous estradiol valerate 1 mg twice daily plus levonorgestrel .25 mg daily; 4) cyclical estradiol valerate 2 mg plus norethisterone acetate 1 mg for 21 of 28 days; or 5) continuous estradiol valerate 2 mg plus norethisterone acetate 1 mg daily. Withdrawal bleeding occurred in all but 1 cyclical patient, but unscheduled bleeding occurred in most continuous patients. In 2 patients, pretreatment hyperplasia had changed to proliferative in 1 and secretory in the other in 6 months of treatment (1 cyclical and the other continous). All pretreatment currettings with proliferative endometrium became secretory endometrium after treatment. It is concluded that cyclical therapy of a combined estrogen and progesterone is least likely to be acceptable to the patient. The advantages of combined versus sequential administrations and optimal doses remains to be determined.