All of the patients developed nausea, vomiting, and confusion while running in a marathon. All had used nonsteroidal anti-inflammatory drugs (NSAIDs), such as ibuprofen, before the race. (NSAIDs can affect the way the body handles salt and water.) On arrival at the emergency room, all patients had so much fluid in their lungs (pulmonary edema) that they required machines called ventilators to help them breathe. They also had low blood levels of sodium and oxygen. Tests of heart function were all normal, indicating that heart abnormality was not responsible for the illness. X-ray pictures in the 6 patients who had them showed swelling of the brain. These 6 patients received treatment with intravenous fluids that contained sodium (hypertonic saline); all recovered completely. The seventh patient died suddenly in the emergency room when his heart stopped working, but the autopsy showed that this patient also had the same problems as the other patients.