Tumour progression is dependent on many factors including antiproteases and proteases released by tumour cells or host cells infiltrating the tumour. In the present study, we evaluated the antiprotease content, namely alpha 2-macroglobulin (A2M) and alpha 1-proteinase inhibitor (A1PI) and neutrophil (PMN) elastase complexed with A1PI, in limited and extended lung cancer patients compared to a nonsmoker and smoker control population. Data showed that A2M and A1PI were increased in the involved lung from limited cancer when compared to normals. In extended lung cancer, A2M content was also increased in the uninvolved side. The concentration of PMN elastase-A1PI complex was increased on both sides in lung cancer patients (10.2 ng.ml-1 in the uninvolved side, 8.2 ng.ml-1 in the involved side) when compared to nonsmokers (1.9 ng.ml-1, p less than 0.001) and smokers (3.8 ng.ml-1, p less than 0.005). This increase was not solely due to the smoking habit. We conclude that antiproteases and PMN elastase complexed with antiprotease are increased in lung cancer area. This increase could result in extracellular changes in lung cancer.