Substance P (SP) infused into the third cerebral ventricle blocks spontaneous ovulation in female rats, probably through catecholaminergic neurons. The studies presented in this paper were undertaken to investigate whether SP exerts its suppressing effect on ovulation in 6-hydroxydopamine (6-OHDA) pretreated female rats. After 8-12 days following 6-OHDA pretreatment female rats were infused, on the day of proestrus, with vehicle and all animals were found to ovulate or with a solution containing 5 nmol of SP and 89% of female rats were then found to ovulate. In the group pretreated with vehicle and subsequently infused with SP, ovulation was found to occur only in 25% of animals. The obtained results indicate that spontaneous ovulation in 6-OHDA-pretreated female rats cannot be blocked by i.c.v. administration of SP, and it may be concluded that SP exerts its suppressing effect through the monoaminergic neurons.