The effects of unilateral and bilateral electrolytic lesions of the dorsal raphe nuclei (DRN) of 30-day-old rats, on the spontaneous and induced ovulation, were analyzed. The bilateral lesion and the lesion on the right side of the DRN delayed the age of first vaginal estrous. None of the animals with bilateral lesion on the DRN ovulated on the day of first estrous (0/8 vs. 12/15, p < 0.05). The ovulation rate in animals with unilateral lesion on the DRN was similar to sham-operated animals, but the number of ova shed by ovulating animals increased in the ovary ipsilateral to the lesion (lesion on right DRN, right ovary: 6.5 +/- 0.5 vs. 4.5 +/- 0.4; lesion on left DRN, left ovary: 6.4 +/- 0.3 vs. 4.2 +/- 0.4, p < 0.05). By the injection of human chorionic gonadotropin, ovulation was restored in rats with a bilateral lesion on the DRN (3/5 vs. 0/8, p < 0.05). The present results suggest that serotoninergic input to the hypothalamus, arising from the DRN, exerts a facilitatory influences on the control of luteinizing hormone release. To explain the increase in the number of ova shed by the left and right ovary, observed in rats with an ipsilateral lesion, we suggest the existence of a neural connection between the DRN and the ovary.