&NA;Plasma norepinephrine (NE) and dopamine&bgr;‐hydroxylase (DBH) levels were measured during the first 7 days after head injury in 48 patients. Blood pressure, pulse, temperature, and Glasgow coma score (GCS) were recorded at the time of sampling for each patient, and the relationships of these to NE and DBH were examined. In patients with multiple trauma. NE levels were usually elevated, regardless of the GCS. In patients with head injury alone, however, NE was proportional to GCS. Alert patients after a brief loss of consciousness (GCS, 14) had normal NE levels. Those in coma had levels as high as 7 times normal. Blood pressure, pulse, and temperature were found to be elevated proportionally to elevations in plasma NE in patients with head injury. The finding of elevated plasma NE in patients with severe head injury raises the possibility of adverse effects of sympathetic hyperactivity in patients with severe head injury, including hypermetabolism, cardiovascular abnormalities, and direct effects of catecholamines on the damaged central nervous system. (Neurosurgery8:10‐14, 1981)