Studies were conducted to investigate the effect of ovine luteinizing hormone (LH) treatment on steroid and LH secretion and ovulation in intact, saline-primed hens and in pregnant mare serum gonadotropin (PMSG)-primed hens. Intact, saline-primed hens, injected 12 hr prior to the first (C1) ovulation of the sequence, responded with fully potentiated preovulatory surges of progesterone (P4) (peak value was 371% above preinjection values), estradiol-17 beta (E2) (117% above baseline), LH (220% above baseline), and premature ovulation. By comparison, those hens injected at the same time prior to the second (C2) ovulation responded with a lesser increase in plasma P4 (peak value was 305% above baseline) and E2 (72% above baseline), and there was no significant increase in plasma LH. Within this group, 4 of 5 hens failed to ovulate prematurely. All groups of PMSG-primed hens had significantly higher preinjection concentrations of P4 and E2, and lower basal concentrations of LH, compared to saline-primed hens. Subsequent to treatment of PMSG-primed hens with 25 or 100 micrograms ovine LH, there was a significant increase in plasma P4 to approximately 200% above preinjection concentrations. By contrast, there was a nonsignificant increase in plasma LH (50% above baseline values) and no significant increase in plasma E2. The ovulatory response following PMSG-priming was greatest in hens injected with 100 micrograms ovine LH (5 of 5 hens ovulated), while 3 of 5 hens injected with 25 micrograms ovine LH and 6 of 6 saline-challenged hens failed to ovulate.(ABSTRACT TRUNCATED AT 250 WORDS)