Rats in which central noradrenergic terminals have been damaged by injecting 6-hydroxydopamine (6-OHDA) into the cerebral ventricular system have been used to study the possible role of noradrenaline (NA) in the effect of trauma on thermoregulation. In non-injured rats the 6-OHDA treatment did not affect the threshold environmental temperature (Ta) for the onset of shivering or the slope of the regression lines relating intensity of shivering to Ta. It raised the core temperature (Tc) threshold for the opening of the A-V anastomoses in the tail. Whereas in normal rats ischaemic limb injury depresses the threshold Ta for the onset of shivering without altering the slope of the regression line, in 6-OHDA-treated rats no depression of the threshold Ta was observed during limb ischaemia but the slope of the regression line was lower. The Tc threshold for the opening of the A-V anastomoses in the tail was the same as in the 6-OHDA-treated controls. The injection of NA into a lateral cerebral ventricle of a normal rat in a 5 degrees environment inhibited shivering and lowered Tc. The 6-OHDA treatment did not induce hypersensitivity to the injection of NA by this route. It is thought that NA is concerned in the central inhibition of shivering during limb ischaemia.