We examined serum levels of neuron-specific enolase by enzyme immunoassay in 29 patients with subarachnoid hemorrhage due to ruptured cerebral aneurysm. Serum neuron-specific enolase levels were significantly higher in patients with a poor neurological status than in patients with a good neurological status on admission, and the greater the amount of subarachnoid blood, the higher the serum neuron-specific enolase level. Patients with a good outcome had low serum neuron-specific enolase levels throughout their courses. Serum neuron-specific enolase levels increased with development of delayed ischemic neurological deficits and, especially in poor outcome patients, high levels persisted until 3 weeks after the subarachnoid hemorrhage.