1 The effect of centrally administered choline on blood pressure was investigated in rats made hypotensive by chemical sympathectomy. Chemical sympathectomy was produced by intravenous (i.v.) injection of 50 mg kg(-1) of 6-hydroxydopamine (6-OHDA). Intracerebroventricular (i.c.v.) administration of choline (50-150 mu g) 2 h after 6-OHDA treatment increased blood pressure and reversed the hypotension in a dose-dependent mariner without affecting heart rate. The presser response was associated with an increase in plasma vasopressin levels.