In order to test possible changes in the stimulating effect of intravenously-infused substance P (SP) on ACTH/cortisol and GH secretion in Parkinson's disease, 10 male parkinsonian patients and 10 age-matched normal controls were infused intravenously for 60 min with SP (1.0 or 1.5 pmol/kg-1/min-1 SP) or normal saline. The circulating levels of ACTH, cortisol and GH were measured during and for 20 min after SP or saline infusion. No untoward side effects or changes in blood pressure were observed during SP infusion in any subjects. In basal conditions and during saline infusion, plasma ACTH and cortisol levels were similar in normal and parkinsonian patients. During SP infusions, ACTH/cortisol concentrations in normal controls rose significantly vs baseline and saline test in a dose-dependent fashion. In contrast, at both SP infused amounts, parkinsonian patients showed ACTH/cortisol levels similar to those observed in the saline test. All subjects showed similar basal concentrations of GH. GH levels rose significantly in the normal controls when the higher dose of SP was infused, but they were not modified by the infusion of the lower dose of SP or saline. At both tested amounts of SP and during saline infusion, GH levels remained unchanged in the parkinsonian subjects. In agreement with previous observations in the literature showing SP abnormalities in the parkinsonian brain, these data fail to show significant effects of plasma SP on the ACTH/cortisol and GH secretory systems in Parkinson's disease.