A long-acting oral estrogen (3-cyclopentyl either of ethinyl estradiol) in doses varying from 2 to 5 mg, and a short acting progestogen were administered orally for 1 day per month to 40 women for 138 trials. The first doses were usually administered between day 21 of the cycle and the onset of menses; day 25 was found to be the most suitable. The progestegen used was one of the following: chlormadinone, dydrogesterone, 6, 17-alpha-dimethyl-6- dehydroprogesterone, or the 18-homologue of norethisterone. Ovulation was inhibited in 78 of the 138 trials and occurred in 32; information was inadequate in 28. No pregnancies occured and side-effects were minimal.