Serum levels of luteinizing hormone (LH), follicle stimulating hormone (FSH), prolactin, estradiol-17β and testosterone were determined in adult rats that were treated in the neonatal period with monosodium L-glutamate (MSG) which has previously been shown to reliably produce destruction of arcuate nucleus perikarya. MSG-treated males had significantly smaller accessory sexual organs (seminal vesicles and ventral prostate) and testes and had significantly lower serum concentrations of FSH and testosterone than sex-matched controls. MSG-treated females had significantly lower serum concentrations of LH, FSH and estradiol-17β. Prolactin levels in MSG-treated rats were no different than sex-matched controls. This marked reduction in gonadal steroid levels (168%) and inappropriately low gonadotropin levels further characterizes the deficit of feedback regulation in the hypothalamic-pituitary-gonadal axis in MSG-treated rats.