The quantitative 2-14C-deoxyglucose autoradiographic method of Sokoloff et al. (1977) was used to measure local cerebral glucose utilization in freely moving developing rats. The animals were studied at 10, 14, 17, 21, and 35 d and at the adult stage. Glucose utilization was very low and quite uniform in 10- and 14-d-old rats, ranging from 20 to 30 mumol/100 gm/min, except in a few posterior areas. Between these 2 stages, rates of glucose utilization significantly increased in 6 areas, among which 4 were belonging to the auditory system. Between 14 and 17 d, glucose utilization significantly changed in 9 structures out of the 68 studied, mainly auditory, visual, parietal, and thalamic areas. Between the stages of 17 and 21 d, glucose utilization was increased by 50 or 100% in all brain structures studied, except in the medial habenula and white matter areas. After weaning time, rates of glucose utilization still significantly changed in 50 areas, widely distributed through all studied systems. Between 35 d and the adult stage, the average rate of glucose utilization did not change and rates of energy metabolism significantly increased in 13 brain areas. In one structure, the medial habenula, glucose utilization was already high 10 d after birth and did not change over the whole studied period. These increases in the rates of glucose utilization are consistent with the behavioral, anatomical, and functional changes known to occur during this period of development in the rat.