In nine patients with severe head trauma, the concentration of neuron-specific enolase in cerebrospinal fluid and in plasma was determined and compared with the activity of creatine kinase and α-hydroxybutyrate dehydrogenase, and with the concentration of lactate. In patients who died of the head trauma, a concentration of neuron-specific enolase of 6.8–64 μg/l in the plasma (reference range: 3.0–6.0 μg/l) and of 2.2–9.0 μg/l in the cerebrospinal fluid (reference range: 0.5–2.0 μg/l) was detected. Investigations of three patients showed that the changes of the concentration of neuron-specific enolase in plasma and in cerebrospinal fluid were independent of each other. Furthermore, the initial concentration of neuron-specific enolase in the plasma after the accident and the dynamics of its changes during the disease show a close relationship to the outcome.