Human blood plasma contains a large number of proteins. New analytical and preparative techniques have so far permitted the isolation of more than one hundred such proteins; about ninety percent of these were first characterized in the last 30 years. The plasma proteins include components of the clotting and complement systems as well as proteinase inhibitors, immunoglobulins, lipoproteins, and carrier proteins. The biological function of some of the plasma proteins is not yet known. Deficiency of one or more plasma proteins usually causes serious health disorders, the best known example being hemophilia. Several biologically active proteins can be gained from blood plasma; these proteins—for example the blood clotting factors—are of great prophylactic and therapeutic importance and allow a better exploitation of the valuable plasma than can be obtained by means of transfusion.