Intraosseous administration of methylene blue may be an emergency alternative to intravascular administration. A 6-week-old female infant (3 kg) presented to the emergency department after a 1-week illness and appeared cyanotic and listless. Oxygen saturation by oximetry was 86% while the patient was receiving oxygen. Vital signs were blood pressure, 107/80 mm Hg; pulse, 190; respirations, 47; temperature, 39.0 degreesC. A metabolic acidosis and a methemoglobin level of 29.3% were present. After several unsuccessful attempts to establish intravenous access, an intraosseous needle was placed in the infant's left tibia. Methylene blue, 1 mg/kg, normal saline solution, and sodium bicarbonate were given intraosseously. The patient's oxygen saturation rose to 98% to 100%, and her cyanosis improved. Three hours later, her methemoglobin level was 8.2%. The child recovered uneventfully and was sent home after 3 days. Intraosseous administration of standard intravenous doses of methylene blue rapidly terminated the effects of acquired methemoglobinemia.