Several traditional vascular risk factors are associated with proinflammatory alterations, including leukocyte activation, and predispose cerebral vasculature to thrombogenesis on inflammatory stimulation. PMN elastase derived from the activated neutrophils might play an important role in injury. This study tries to elucidate the involvement of activated polymorphonuclear neutrophil proteolytic activity in the pathophysiology of ischemic stroke. Levels of PMN elastase/alpha 1-proteinase inhibitor complex (PMN-E/alpha1-PI) were measured in 145 patients (mean age 72.4+/-6.3) with first ischemic stroke from the onset day (day 0) to 7 days after onset (day 7) and 260 control subjects drawn matched for age, sex. Quantitative estimation of the plasma levels of the PMN-E/alpha1-PI complex was carried out with a highly sensitive enzyme-linked immunoassay (ELISA). Plasma PMN elastase levels were statistically significantly higher on 7 day patients (384.7+/-31.4 microg/L vs 216.5+/-26.8 microg/L on day 0; p<0.01) than in those without ischemic stroke (67.4+/-5.2 microg/L). Plasma PMN elastase may be a well-characterised and sensitive inflammation marker, and it is associated with endothelial dysfunction. PMN elastase can be used as a measure for the activity of granulocytes during an inflammatory response. Furthermore it may be possible to treat such disorders with proteinase inhibitors.