1. Ventral noradrenergic projections (VNAB) from lateral tegmental (A 1 , A 2 ) and dorsal noradrenergic projections (DNAB) from the coeruleal (A 6 ) as well as A 1 cell groups in the brain-stem of the rat were lesioned by intracerebral injection of 6-hydroxydopamine. 2. A marked increase in plasma renin activity and adrenaline concentrations followed haemorrhage (0.5 ml/100 g body weight) in the sham-operated rats. VNAB-lesioned rats showed a similar response to the sham-operated controls, but in DNAB-lesioned animals the rise of plasma renin was markedly attenuated.