Serum concentrations of luteinizing hormone (LH) follicle-stimulating hormone (FSH), prolactin (PRL) and testosterone were measured by radioimmunoassay in male Wistar rats: (a) Four days after a septal lesion (n = 19) and (b) Just following electrical stimulation of the septum (n = 15). Septal lesions induced a significant decrease in serum LH (16.37 +/- 2.01 vs. 30.27 +/- 2.08 ng/ml; p less than 0.001) and testosterone concentrations (0.53 +/- 0.05 vs. 1.01 +/- 0.14 ng/ml; p less than 0.02). No significant changes were observed for FSH or PRL levels. Electrical septal stimulation induced an increase in serum levels of LH (211.5 +/- 46.4 vs. 29.6 +/- 11.5 ng/ml; p less than 0.01) and FSH (703 +/- 83 vs. 378 +/- 57 ng/ml; p less than 0.01), without changes in PRL or testosterone concentrations. From these data we conclude that in male rats the septum may play a role in the mechanisms controlling gonadotropins release by the anterior pituitary gland.