The administration of five subcutaneous 250-microgram doses of lutienizing hormone (LH)-releasing hormone (LHRH) at 4-hour intervals, the first injection being given at 8 A.M. on 1 or 2 consecutive days between days 1 and 9 following the LH surge in normal women, shortened the luteal phase from 1 to 4 days in 16 of 17 treatment cycles. There was a better efficiency of treatment when LHRH was administered on days 6 to 9 after the LH surge as compared with days 1 to 5. In fact, the luteal phase was shortened from 3.3 +/- 0.2 days versus 1.4 +/- 0.2 days (P less than 0.01) and the serum progesterone level was decreased to 44% +/- 6% versus 71% +/- 6% of control levels (P less than 0.01) when the neurohormone was injected late as compared with early in the luteal phase. The present data raise the possibility of a luteolytic effect of LHRH in normal women and indicate the interest of such a near-physiologic approach for the control of luteal function and time of appearance of menses.