The prognostic value of ubiquitin levels in cerebrospinal fluid (CSF) was studied in human global brain ischemia (anoxic-ischemic encephalopathy). Twenty four samples were collected from 13 patients who were resuscitated from cardio-pulmonary arrest and survived for at least 1 day. The outcome was classified according to the Glasgow Outcome Scale (GOS1-5). The ubiquitin levels (normal: 14.3 +/- 1.1 ng/ml, mean +/- S.E.M.) in neurologically symptomatic patients (GOS1-4) were 151 +/- 32.5 ng/ml on day 1-2 and elevated to 1,960 +/- 849 ng/ml on day 3-4. The Spearman's rank correlation of ubiquitin levels on day 3-4 and the GOS was -0.855, showing a better correlation than CSF neuron-specific enolase levels (r = -0.846). Ubiquitin is a heat shock protein associated with the degradation of abnormal cellular proteins. Thus, the elevation of CSF ubiquitin levels represents both its overproduction by a cytoprotective response to brain ischemia and its leakage from the damaged tissue. The present study suggests that the measurement of CSF ubiquitin level is useful for the early prognostic assessment of global brain ischemia.