The administration of LH-RH in a pulsatile regimen (100 ng i.v./h for 48 h) to acyclic ewes 26-30 days post partum increased plasma LH concentrations, and both the frequency and amplitude of plasma LH pulses. In 12/14 ewes these increases were followed by plasma LH surges similar to the preovulatory surges observed in 10 control cyclic ewes. Subsequent luteal function in the post-partum ewes was deficient. Plasma progesterone was detected in 7/12 post-partum ewes showing plasma LH surges. The concentrations were lower (1.3 ± 0.2 ng/ml) and detected for shorter periods (3-10 days) than in cyclic ewes (2.4 ± 0.2 ng/ml, 12/15 days). In the post-partum ewes the increases in plasma LH concentrations before the LH surge were higher but of shorter duration than in the cyclic ewes. The inadequate luteal function in the post-partum ewes could therefore have been due to inappropriate LH stimulation of the ovary before the LH surge.