1 Intracerebroventricular (i.c.v.) injection of choline (25 - 150 mu g) increased blood pressure in rats made acutely hypotensive by haemorrhage. Intraperitoneal administration of choline (60 mg kg(-1)) also increased blood pressure, but to a lesser extent. Following i.c.v. injection of 25 mu g or 50 mu g of choline, heart rate did not change, while 100 mu g or 150 pg i.c.v. choline produced a slight and short lasting bradycardia. Choline (150 mu g) failed to alter the circulating residual volume of blood in haemorrhaged rats.