The complement system (C) is composed of group of plasma proteins which under certain conditions react with each other sequentially, resulting in the formation of highly specialized proteases. By their action multimolecular complexes are assembled, and when these events occur on the surface of some cells, the membrane function is impaired and the cell will lyse. Fragments and complexes appearing on activation of the complement system participate in other important biological activities such as chemotaxis, opsonization and in histamin release from mast cells and basophilic granulocytes.