We assessed the effects of age on cholinergic regulation of the hypothalamic-pituitary-adrenal axis and other neuroendocrine systems by measuring the plasma cortisol and beta-endorphin responses to an infusion of the centrally active cholinesterase inhibitor physostigmine (0.0125 mg/kg) in 12 healthy older men (68 +/- 1.7 yr) and 9 healthy young men (25 +/- 1.4 yr). We also measured the responses to physostigmine of plasma GH, arginine vasopressin, epinephrine, and norepinephrine (NE). As estimated by comparing calculated areas under the curve, older subjects had greater cortisol (P = 0.02) and beta-endorphin (P less than 0.01) secretory responses, but a reduced GH (P less than 0.01) secretory response. The arginine vasopressin response did not differ between groups. By analysis of variance, older subjects also had a greater epinephrine response (P = 0.01). Older subjects had higher basal NE concentrations (P less than 0.05), but NE responses to physostigmine did not differ between groups. These findings suggest age-related enhancement of the cholinergic stimulatory regulation of the hypothalamic-pituitary-adrenal axis and adrenal medulla. They also confirm previous reports of reduced GH secretory response with aging in normal men.