Background: Proteases play a regulatory role in a variety of pathologies including cancer, pancreatitis, thromboembolic disorders, viral infections and many others. One of the possible strategies to combat these pathologies seems to be the use of protease inhibitors. LC-pi I, II, III and IV (Lavatera cashmerian-protease inhibitors) have been found in vitro to strongly inhibit trypsin, chymotrypsin and elastase, proteases contributing to tumour invasion and metastasis, indicated possible anticancer effects. The purpose of this study was to check in vitro anticancer activity of these four inhibitors on human lung cancer cell lines. Material and Methods: In order to assess whether these inhibitors induced in vitro cytoxicity, SRB assay was conducted with THP-1 (leukemia), NCIH322 (lung) and Colo205, HCT-116 (colon) lines. Results: LC-pi I significantly inhibited the cell proliferation of all cells tested and also LC-pi II was active in all except HCT-116. Inhibition of cell growth by LC-pi III and IV was negligible. $IC_{50}$ values of LC-pi I and II for NCIH322, were less compared to other cell lines suggesting that lung cancer cells are more inhibited. Conclusion: These investigations might point to future preventive as well as curative solutions using plant protease inhibitors for various cancers, especially in the lung, hence warranting their further investigation.