Human Leucocyte Elastase (HLE) is a serine protease, which is released from neutrophils in response to inflammatory stimuli. Under normal conditions, the body protects itself from the potential damaging effects from extracellular HLE with the endogenous α1-proteinase inhibitor. Sometime, the action of these endogenous inhibitors seems to be insufficient because there is an unbalance between HLE and antiprotease levels which causes a greater proteolitic activity of this enzyme. This unbalance comes out from an inhibitor decrease, often due to a genetic deficit. The excess HLE, produced by this unbalance, hydrolyzes elastin, the structural protein which gives to the lungs their elasticity, thus initiating and/or contributing to the development of diseases such as pulmonary emphysema, chronic bronchitis, adult respiratory distress syndrome, rheumatoid arthritis, atherosclerosis, cystic fibrosis, chronic bowel disease, and other inflammatory disorders. For these reasons, we are carrying out in a vitro screening programme of new molecular entities ’ s evaluation such as Human Leucocyte Elastase (HLE) inhibitors. In this work we have processed beta-lactams derivatives by examining azetidinone structures, replaced in position 3, in order to find molecules possessing both a satisfactory inhibition of the HLE and a good chemical stability. The results of our experiments indicate that compounds 3d-3e-3f and 3h (450 -ÊM) were able to induce a significative inhibition of HLE (% of inhibition was 30, 45, 57 and 69, respectively, P < 0.01) indicating that these ..-lattamics could be potential inhibitors of HLE.