Cerebral oxygen uptake was correlated with electroencephalographic (EEG) frequency and amplitude in 87 isolated canine brains. Group I (71 brains) was perfused with diluted blood and Group II (16 brains) was perfused with whole blood equilibrated with oxygen at various partial pressures. The EEG's were classified as follows: A, highest frequency greater than or equal to 17 Hz, alpha (8-13 Hz) amplitude less than 50 muv, delta (less than or equal to 3.5 Hz), amplitude less than 100 muv; B, highest frequency greater than or equal to 17 Hz, alpha amplitude greater to or equal to 50 muv, and/or delta amplitude greater than or equal to 100 muv. C, highest frequency 8-16 Hz, alpha amplitude greater than or equal to 25 muv, and delta amplitude greater than 100 muv, D, highest frequency 0.5-16 Hz, alpha, if present, amplitude less than 25 muv, and/or delta amplitude less than 100 muv, and E, highest frequency 0-16 Hz, alpha, if present, amplitude less than 10 muv, and/or delta amplitude less than 15 muv. The Group I oxygen uptakes in ml/100 g of brain per min+/-SE for the five EEG classifications were A, 4.39+/-0.06, B, 4.13+/-0.08, C, 3.76+/-0.09, D, 3.40+/-0.12, and E, 2.55+/-0.06, whereas the corresponding Group II values were A, 4.64+/-0.22, B, 4.28+/-0.15, C, 3.82+/-0.24, D, 3.39+/-0.40, and E, 1.38+/-0.42. As the EEG deteriorates, cerebral oxygen uptake tends to decrease in a significant and parallel manner in both the diluted and whole blood groups.