Ecotin (E. coli serine protease inhibitor) inhibits pancreatic serine proteases. This protein inhibits chymotrypsin, trypsin, elastases, factor X, kallikrein as well as a variety of other proteases. The strength of inhibition does not appear to be correlated with a particular protease specificity. Recombinant E. coli Ecotin protein, fused to His-tag at N-terminus, was expressed in E.coli and purified by using conventional chromatography techniques.