A 60-year-old chemist was admitted two hours after voluntary intake of 600 mg KCL. Upon admission he was in deep coma and bradypneic but non-cyanotic. Arterial blood gas analysis showed severe lactic acidosis; blood cyanide concentration was well above the lethal level. The patient was intubated and artificially ventilated with highly hyperoxic mixtures. Specific treatment included sodium nitrite and sodium thiosulfate. The patient recovered without sequelae despite excessive methemoglobinemia. The hemodynamic study upon admission showed a hyperdynamic status associated with low peripheral resistances and normal filling pressures, a profile similar to that described in response to acute anoxia in experimental animals.