Recombinant serpins, members of a serine protease inhibitor superfamily, are now available. Severe serpin A1 deficiency leads to several clinical complications, such as pulmonary emphysema, juvenile hepatitis, cirrhosis, and hepatocellular carcinoma. Because of its protease targets and regulated expression patterns, serpin A5 has been proposed to play a role in processes such as blood coagulation, fertilization and carcinogenesis. Hereditary and acquired serpin C1 deficiency causes an increased thrombotic tendency, while congenital serpin D1 deficiency is a potential risk factor for thrombosis.