Regional glucose distribution in brain slices was assessed by a bioluminescence technique. The reaction is based on light emission of luminiferous marine bacteria, Vibrio fischeri, induced by NADPH. Freeze-dried brain slices were covered by a solution which contained: (a) enzymes and substrates for glucose oxidation and NADPH formation and (b) an extract of Vibrio fischeri for the bioluminescence reaction. Glucose-induced bioluminescence was recorded on photographic film. Patterns of regional decrease in glucose concentration were demonstrated in cat brains after occlusion of the left middle cerebral artery. This decrease correlated well with a concomitant depletion of ATP and an increase in NADH-fluorescence.