The effect of sodium cyanate (25, 50, 75, and 100 mg/kg body weight i.p. daily for 10 days) upon cerebral metabolism and the EEG of Wistar rats was studied. This treatment resulted in a dose-related carbamylation of hemoglobin and left shift in the oxygen dissociation curve. Animals receiving the highest dose of cyanate developed a significant systemic metabolic acidosis. In brain there was dose-dependent decrease in phosphocreatine, TCO2 and cytoplasmic NADH/NAD+ ratio, reflecting the calculated drop in intracellular pH. Glucose levels were elevated despite a normal calculated energy charge, which suggests a balanced slowing of the energy-producing and energy-utilizing systems. The higher doses of cyanate produced spontaneous seizure activity on the EEG.