Enolase is an enzyme involved in glycolysis and neurospecific enolase (NSE) has two types of isoenzyme (alpha gamma and gamma gamma enolase). Found in nerve cells and axons, the NSE is reported to be released into the serum and cerebrospinal fluid following nerve injury. We recently analyzed serum NSE levels in 47 patients with solitary head injury who were transported to our center immediately after injury. There were 35 men and 12 women, with a mean age of 35.1 years. In each case, blood was sampled within 8 hours after injury. Serum NSE was measured and analyzed in relation to the level of consciousness (Japan Coma Scale) upon admission, the modified Araki's classification, the presence or absence of skull fracture, findings from computed tomography (CT) scans and the prognosis according to the Glasgow outcome scale. Differences were compared by t-test to determine significance. When the level of consciousness was compared with the serum NSE level upon admission, the NSE level was significantly higher in patients showing a three digit code disturbance of consciousness than in the other patients (p < 0.005). When NSE was analyzed in relation to the modified Araki's classification, the NSE level for the prolonged type with focal signs was higher than the NSE level for any other type (p < 0.001 compared to the transient type). The NSE level was significantly higher in patients with skull fracture than in patients without skull fracture (p < 0.01). The NSE level was significantly higher in patients showing contusion on CT scans than in patients without contusion (p < 0.005).(ABSTRACT TRUNCATED AT 250 WORDS)