The toxicity of hydrogen sulfide is thought to be due primarily to reversible inactivation of the respiratory enzyme, cytochrome oxidase, with resultant inhibition of aerobic metabolism. A patient with severe hydrogen sulfide poisoning and consequent profound metabolic acidosis was treated successfully with nitrites and oxygen. The nitrite-induced methemoglobin, by competititively binding the toxic hydrosulfide anion until detoxified, presumably reactivated and protected cytochrome oxidase and thereby aided the patient''s recovery by enhancing aerobic metabolism. His rapid recovery adds clinical support to the efficacy of nitrite therapy in sulfide poisoning. Severe cases of sulfide poisoning should be treated with nitrite-induced methemoglobinemia in addition to vigorous supportive care.