There is a practical way to measure metabolism, flow, and function in a localized area of brain serially in the same animal. Our preliminary anatomical and angiographical studies have indicated that certain pairedcerebral veinsdrain only blood from cortex supplied by easily identified cerebral arteries. These veins have been cannulated bilaterally without altering flow in their territory of distribution. When compared to the arterial concentrations of the substances and the regional blood flow, one can calculate the regional metabolic rate of the tissue in this inflow-outflow system (vascular-metabolic unit). This system can be subjected toischemia, trauma, and pharmacological and neurophysiological alterations. In addition, it is accessible for measurement of electrical activity, surface fluorometry, and sampling for histological and cortical biochemical analysis.