Dopamine Beta Hydroxylase (DBH) activity was determined in 24 deeply comatose patients enrolled in the Collaborative Study of Cerebral Survival. All patients had been without cerebral responsiveness or spontaneous respirations for at least 15 minutes. Patients were examined, EEGs performed and blood for DBH drawn within 24 hours of the cerebral insult. DBH activity was lower in the deeply comatose patients than in a group of 51 age matched normal individuals. It is postulated that destruction or inactivation of the central nervous system (CNS) and particularly of the cerebrum may result in lowered serum DBH activity through decreased activation of sympathetic nerve terminals.