Survival after severe hyponatremia (serum sodium 125 mEq/l) and hypochloremia (serum chloride 78 mEq/l) is described in an adult with acute leukemia who received toxic doses of vincristine. Transient confusion and prostration accompanied the electrolyte abnormalities. Laboratory evidence of CNS leukemia was not present. The patient with supportive care improved rapidly within two days as the electrolytes gradually returned toward normal; the electrolytes became entirely normal on the fifth day. Stringent sodium chloride replacement was not required to correct the hyponatremia and hypochloremia. Although rare, vincristine-induced hyponatremia and hypochloremia constitute a serious complication that warrants prompt recognition and supportive medical care.