Proteinase 3 (PR3), together with other serine proteases, such as neutrophil elastase (NE) and cathepsin G (CG), regulates inflammatory and immune responses. However, in comparison with NE and CG, there is increasing evidence that PR3 functions significantly differ. In particular, PR3 can bind to cell membranes and such membrane-bound PR3 (mbPR3) might be differently involved in the activation of cytokines, growth factors, cellular receptors, and in the regulation of cell apoptosis. For instance, PR3 membrane binding can block some "eat me" signals, notably, phosphatidylserine membrane lipid, and facilitate non-resolving inflammation. Based on the clear evidence that PR3 membrane binding affects the biological functions of PR3, we designed peptidomimetic inhibitors that can remove mbPR3 from the membrane surface in vitro without influencing PR3 catalytic activity. Such inhibitors, which specifically target PR3 binding to membranes, are still lacking. In particular, we found peptidomimetics that inhibit binding of PR3 to POPC:PS liposomes, which mimic the biological environment of PR3.