The ovary is innervated by noradrenergic and peptidergic fibers. Treatment of neonatal rats with antibodies to nerve growth factor (NGF Ab) resulted in failure of the sympathetic (noradrenergic and neuropeptide-Y) nerves to develop. Partial loss of sensory innervation, represented by calcitonin gene-related peptide fibers, was also observed. Follicular growth was stunted, and production of androgens and estradiol was reduced. The timing of first ovulation was delayed, estrous cyclicity was disrupted, and fertility was compromised. Plasma LH levels were elevated, and LH pulsatility was enhanced, suggesting primary ovarian failure. A normal appearance of tyrosine hydroxylase-, LHRH-, and neuropeptide-Y-immunoreactive neurons in the hypothalamus, as determined by immunocytochemistry, suggested that neonatal immunosympathectomy did not directly affect hypothalamic reproductive function. In vitro release of LHRH from median eminence nerve terminals in response to prostaglandin E2 was, however, reduced in NGF Ab-treated rats. Normalization of the response by prior in vivo exposure of the animals to physiological estradiol levels, suggested that the diminished LHRH output was due at least in part to estrogen deficiency. Although ovarian dysfunction induced by immunosympathectomy may be related to alterations in vascular tone, the striking loss of perifollicular noradrenergic innervation caused by NGF Ab suggests that the absence of the nonvascular norepinephrine stimulus to follicular steroidogenesis is a primary factor responsible for the alterations observed. The results indicate that development of the sympathetic innervation of the ovary is NGF dependent and that NGF, by supporting the differentiation and survival of the innervating neurons, contributes to the acquisition of mature ovarian function.