A technique is described for the chronic measurement of cerebral blood flow in conscious, unrestrained rodents, utilizing laser doppler flowmetry (LDF) removably coupled to an optical fiber permanently implanted into brain tissue by established stereotaxic procedures. Changes in relative blood flow in response to a range of pharmacological and behavioral challenges were measured in the hippocampus (HBF) and striatum (StBF) 24-72 h and up to 28-32 days after surgical implantation of the optical fiber. Intraseptal microinfusion of L-glutamate in artificial cerebrospinal fluid 48-96 h and 28-32 days after surgery increased HBF. Pentobarbital (Nembutal) and urethane anesthesia decreased HBF. On the day of euthanasia under urethane anesthesia, HBF was demonstrated to be responsive to alteration of blood CO2 via hyper/hypocapnia, and autoregulation was demonstrated in response to hypovolemic hypotension. In behavioral experiments, blood flow was found to increase with activity and locomotion, as well as during paradoxical (PS) and slow-wave sleep (SWS). The greatest increase in CBF was measured during PS. Although basal levels of blood flow were similar between regions, the increase in blood flow during PS was greater in the hippocampus. This simple procedure enables real-time measurement of qualitative changes in regional cerebral blood flow during behaviors in conscious, unrestrained animals. The observation that constancy of measurements was obtained for 1 month enables within-subject analysis in longitudinal studies and reduces the number of animals required for investigations.