Somato sensory evoked potentials (SEP), cerebral blood flow and cerebral metabolism were studied in seven rhesus monkeys before and after a right occipito-frontal missile injury with an air rifle. The sensory evoked potential was present shortly after injury though markedly altered in shape. There was a very close correlation (r2 equal to 0.83) between SEP and cerebral blood flow on the uninjured side five minutes after injury. On the injured side, this was also noted but the amplitude of the SEP was much smaller, perhaps due to direct injury. If the flow in either hemisphere fell below 15-20 mls/100 gm/min, the evoked response disappeared, but in several animals a subsequent increase in flow was associated with a return of electrical activity. There was no correlation with cerebral perfusion pressure or cerebral metabolic rates for oxygen or lactate production, though it is likely that this is not due to physiological reasons but rather methodological. It might be inferred from these results that adequate flow is vital for the preservation and return of electrical activity following brain injury.