The [14C]deoxyglucose [Sokoloff et al., J. Neurochem. 28, 897-916 (1977)] and [6-14C]glucose [Hawkins et al., Am. J. Physiol. 248, C170-C176 (1985)] quantitative autoradiographic methods were used to measure regional brain glucose utilization in awake rats. The spatial resolution and qualitative appearance of the autoradiograms were similar. In resting animals, there was no significant difference between the two methods among 18 gray and three white matter structures over a fourfold range in glucose utilization rates (coefficient of correlation = 0.97). In rats given increasing frequencies of photoflash visual stimulation, the two methods gave different results for glucose utilization within visual pathways. The linearity of the metabolic response was studied in the superior colliculus using an on-off checkerboard stimulus between 0 and 33 Hz. The greatest increment in activity occurred between 0 and 4 Hz stimulation with both methods, probably representing recruitment of neuronal elements into activity. Above 4 Hz, there was a progressive increase in labeling with [14C]deoxyglucose up to 1.7 times control at 33 Hz. With [6-14C]-glucose, there was no further increment in change above a 30% increase seen at 4 Hz. Measurement of tissue glucose revealed no drop in the visually stimulated structures compared to control. We interpret these results to indicate that, with increasing rates of physiological activity, the products of deoxyglucose metabolism accumulate progressively, but the products of glucose metabolism are removed from brain in 10 min.