The pathogenesis of recurrent aphthous stomatitis (RAS) is poorly understood. The neutrophil elastase is implicated in tissue damage occurring in the course of several chronic inflammatory conditions. This strong proteolytic enzyme may be also a sensitive indicator of inflammation. EDTA-treated blood was obtained from 12 patients with the acute stage of minor RAS (aged from 1.5 to16 years, 7 girls and 5 boys) and 15 healthy children. The plasma concentration of neutrophil elastase in complex with alf&#945;1-proteinase inhibitor (NE-&#945;1PI) was measured by ELISA methods. All RAS patients had significantly (p<0.00001) higher levels of NE-&#945;1IP (av. 377.96&#177;306.52; median: 226.19 &#181;g/L) compared to the control group (av. 55.90&#177;20.31; median: 57.53 &#181;g/L). Our data suggest that NE-&#945;1IP may be a useful indicator of neutrophils activation in RAS patients and may be also involved in pathogenesis of this disease. These observations could have implications for development of new therapeutic strategies in the future.