Cerebral blood flow (CBF) was measured by [14C]butanol indicator fractionation in 10 rats given intraventricular injections of 6-hydroxydopamine (6-OHDA) compared to 8 saline-injected controls. Rats treated with 6-OHDA displayed an 83% reduction in cortical norepinephrine (NE) levels. CBF was significantly increased in 6-OHDA-treated rats compared to controls (average whole brain blood flow of 126.0 +/- 8.3 and 97.1 +/- 10.6 ml.min-1.10(-2)g-1 respectively, P less than 0.05). These studies suggest that noradrenergic innervation of the brain and cerebral microvasculature exerts a moderating effect on resting CBF.