A one-step procedure for human leukocyte elastase purification using an affinity adsorbent based on protein soybean Bowman-Birk proteinase inhibitor has been developed. The leukocyte elastase was purified 70-fold with a 70-100% yield. The enzyme preparations did not contain cathepsin G and displayed a high specific activity. The soybean Bowman-Birk type inhibitor effectively inhibited the elastin hydrolysis by leukocyte elastase both when the enzyme and the inhibitor were simultaneously added to the substrate and after preliminary elastase adsorption on elastin. The inhibitory effect was preserved at high degrees of elastin hydrolysis.