Electrical shock treatment produces a rapid loss of high energy phosphates in rat brain. The [ATP]/[ADP] ratio decreases to one-third of its control value within 10 s. The ammonia content increases 3-fold during the first minute after starting the stimulus. The total adenine nucleotide plus adenosine content of brain decreases an equivalent amount of hypoxanthine-containing compounds appears. Adenosine, inosine, and hypoxanthine accumulate, and there is a transitory accumulation of adenylosuccinate. The contents of ATP and creatine phosphate, and the [ATP]/[ADP] ratio, are rapidly restored to control values, but other metabolite contents are restored more slowly. The transient rise in adenylosuccinate and IMP provides evidence that the ammonia production is due in part, and possibly in whole, to the operation of the purine nucleotide cycle.