This study was undertaken to evaluate the brain hemodynamics of the primate (Macaca mulatta) in the conscious and anesthetized state. A polarographical circuit was utilized for repetitive measurements of local and average total cerebral blood flow in the conscious state, during analgesia/paralysis, and in the anesthetized state. The electrochemical considerations and in vitro testing are described. Blood flow values were highest in sensory and motor cortex (92.5 ± 3.5 ml/100 gm per minute and 86.2 ± 2.6 ml/100 gm per minute), while there were no significant differences found between other regions of association cortex. Mean deep gray matter blood flow values ranged between 57.6 ± 3.8 and 69.2 ± 3.4 ml/100 gm per minute. The mean local blood flow for the centrum semiovale was found to be 19.5 ± 1.2 ml/100 gm per minute and that for pontine tegmentum was 58.1 ± 3.5 ml/100 gm per minute. At any one electrode locus, at steady state levels of arterial blood gases, the reproducibility of blood flow ranged between 11% and 18%. Seventy-five percent nitrous oxide/25% oxygen in combination with a paralytic agent produced a questionably significant drop in caudate nucleus blood flow. The depressant effects of anesthetic doses of sodium pentobarbital on cerebral blood flow, however, were significant at most electrode sites. These data indicate that the measured blood flow rates within small brain volumes are critically affected by barbiturate anesthesia and seriously question the value of published reports in which these agents were utilized.