Patient A. On August 19, 2011, a man aged 33 years was taken by ambulance to a local emergency department after he collapsed in a fast food restaurant. He reported feeling lightheaded and nauseated 15 minutes after consuming a soft drink with his friend (patient B). When questioned, patient A initially said he had not ingested medications or illicit drugs. On physical examination, he appeared cyanotic with altered mental status, and his blood oxygen saturation measured by pulse oximetry was 86% on 100% supplemental oxygen by nonrebreather mask. Blood drawn for laboratory testing was chocolate-brown. Arterial blood pH was 7.43, the pCO was 35 mm Hg, and the pO was 222 mm Hg. His methemoglobin concentration was 66.7% (normal: 1%-3%), his hemoglobin concentration was 14.3 g/dL (normal: 13.8-17.2 g/dL), and his platelet count was 338,000/mm3 (normal: 150,000-400,000/mm3). The Oregon Poison Center was consulted and recommended administration of 1 mg/kg body weight methylene blue intravenously. The patient was admitted to the hospital intensive-care unit.