Cerebral blood flow (CBF) and blood flow (BF) in extracerebral head structures were measured during the sleep-wake cycle in rats using radioactive microspheres. While no statistically significant changes occurred in the transition from Waking to quiet sleep (also referred to as synchronized or non-REM Sleep), CBF increased significantly in active sleep (AS, also referred to as desynchronized or REM Sleep) in all structures considered, with the sole exception of the cerebellum. In extracerebral head structures, no significant state-dependent BF changes were found. Factor Analysis however extracted a common factor accounting for BF variability in the external carotid circulation. This factor was uncorrelated with CBF changes in AS, suggesting independent regulation of the two vascular beds in this sleep state.