We examined the concentrations of lactate dehydrogenase in the cerebrospinal fluid of 25 patients with strokes and 15 patients with transient ischemic attacks less than or equal to 8 hours after the onset of the vascular event and in a control group of 21 patients. We found significantly higher concentrations in the stroke patients (40.9 +/- 14.5 units/l) than in the transient ischemic attack patients (11.8 +/- 2.9 units/l, p less than 0.001) and the controls (11.2 +/- 6.7 units/l, p less than 0.001). Among the stroke patients, we found a significantly higher lactate dehydrogenase concentration in those with cortical strokes (n = 12, 50 +/- 12.3 units/l) than in those with lacunar white matter infarcts (n = 5, 26.4 +/- 6.5 units/l; p less than 0.001) and those with basal ganglia infarcts (n = 8, 36.37 +/- 11.7 units/l; p less than 0.05). Our study offers a supplementary examination for diagnosing cortical or subcortical infarction during the early stage of the event, with the possibility of distinguishing precisely stroke from transient ischemic attack during the first hours after onset of the event.