The deoxyglucose technique for the measurement of local cerebral glucose metabolism (LCMRgl) has been widely applied in animals utilizing 14C-deoxyglucose and in humans employing 18F-fluorodeoxyglucose. Repeat studies in humans over a relatively brief period of time have not been possible because of the 110-min half-life of fluorine-18. With the synthesis of 11C-deoxyglucose it has now become possible to utilize this short-lived (20 min) tracer for the measurement of LCMRgl and to determine its variability within subjects over a 2-h period. The kinetic rate constants for 11C-deoxyglucose were determined for gray and white matter and found to be very similar to those for 18F-fluorodeoxyglucose, suggesting that these two analogues of glucose have similar affinities for the facilitated transport system and are similar substrates for hexokinase in the brain. The coefficient of variation of repeated measurements of LCMRgl in a series of six normal subjects was 5.5% to 8.7% for various gray matter structures and 9.7% and 14.0% for white matter structures. The pattern of cerebral metabolic rates is relatively constant in a given individual when the conditions of the study are unchanged. The ability to make repeat measurements in the same subject reduces the variance due to between-subject differences, allowing smaller changes in LCMRgl to be detected with confidence.