Cellular respiration in vitro was studied in cerebral cortical tissue from rats 2-60 days of age. Respiration was measured polarographically over the temperature range 34-44 degrees C in tissue slices in a basal condition; maximally stimulated by an uncoupler of oxidative phosphorylation, dinitrophenol; and inhibited by a blocker of mitochondrial oxidative phosphorylation, oligomycin. Basal respiration at 34 degrees C increased about 80% between 7 and 30 days of age. Oligomycin-insensitive respiration did not change with age. Dinitrophenol-stimulated respiration was unchanged from 2 to 10 days and then increased over 100% between 10 and 15 days of age. The Q10 for dinitrophenol-stimulated respiration increased from a value of 1 in tissue from rats 2-10 days of age to about 2 in tissue from rats 15 days and older. Our results confirm the previously reported maturational increases in basal respiration and in respiratory capacity in rat cerebral cortical tissue. The maturational increase in maximal respiratory capacity occurs in a short age interval coincident with a marked increase in the Q10 for the hyperthermic temperature range. Both these properties may be important in the increasing resistance to hyperthermia-induced seizures and their functional sequelae in the rat pup.