Unidirectional glucose transport and diffusion and net glucose uptake were measured before, during and after perfusion of the isolated canine brain with anoxic blood. An indicator dilution technique with 22Na as the intravascular marker was used to measure unidirectional transport of d-[6-3H]glucose from blood into brain while the rate of unidirectional diffusion was estimated from similar studies using 22Na and d-[6-3H]fructose. Net glucose uptake was calculated by multiplying the arteriovenous concentration difference by the plasma flow rate. During the first 2 min of anoxia, the rate of net glucose uptake more than doubled, but by 10 min of anoxia it had declined to near the pre-anoxic level. Net uptake did not change significantly between 10 and 30 min of anoxia nor during the first hour of post-anoxic recovery. The kinetics of unidirectional glucose transport were unchanged after 1 min of anoxia; however, after 10 min, unidirectional transport was decreased to an average of 39% of the control rate. After 1 h of recovery from 30 min of anoxia, transport was 59% of the control rate. The rate of simple diffusion of glucose was unchanged during and after anoxia. It was concluded that the initial increase in net glucose uptake is due to a decrease in the rate of unidirectional efflux of glucose from the brain as a result of reduced brain glucose levels. The subsequent decrease in net uptake is caused by an impairment of unidirectional glucose transport. These data indicate that transport of glucose from the blood to the brain may be an energy dependent process.