We have studied the effect of administration of L-monosodium glutamate (MSG) to neonatal rats on gonadotroph morphology and gonadotrophin secretion in the prepubertal male rat. Rats were injected with MSG (4 mg/g body weight) or with 0.1 ml saline/10 g body weight on days 1, 3, 5, 7 and 9 of life (day of birth = day 0) and were used for experiment on day 40. Trunk blood was collected from 8 saline- and 9 MSG-injected rats for assay of serum luteinizing hormone (LH) and follicle-stimulating hormone (FSH) concentrations. One-half of the anterior pituitary gland was assayed for LH and FSH concentrations and the other half was placed in culture medium for a 30-min preincubation and then placed in fresh medium for a 2-hour incubation (basal LH and FSH release). An additional 4 rats in each group were killed and the pituitary glands were prepared for histological examination and immunocytochemical staining of LH and FSH cells and morphometric examination of these cells at the light microscopic level. The morphometric analyses were compared with those performed previously by us on adult male rats.(ABSTRACT TRUNCATED AT 250 WORDS)