Members of the serine protease family play a role in carefully controlled processes, such as blood coagulation, fibrinolysis, complement activation, fertilization, and hormone production. The enzymatic activity of the serine proteases is regulated in part by serpins, serine protease inhibitors. Serpin dysfunction is associated with various disorders, including emphysema, blood clotting disorders, cirrhosis, Alzheimer disease, and Parkinson disease. Zserp11 is a new member of the serine protease inhibitor family.