The discovery of the kinin system is not recent, but its study in clinical field has been done only in the last years. This system is composed by substrates (kininogens) and plasma and tissue kallikreins are the specific activators of these substrates producing two vasoactive peptides called bradykinin and kallidin. The biologic effects of kinins are mediated by specific receptors called B1 and B2. The activation of this system is particularly important in blood pressure regulation and in inflammatory reactions. The kinin system is involved in many clinical situations including respiratory allergic reactions, septic shock, hypertension and its treatment, hypotensive transfusion reactions, heart diseases, pancreatitis, hereditary and acquired angioedema, Alzheimer's disease and liver cirrhosis with ascites. The study of the kinin system in clinical field, which had been limited by methodological difficulties, has now received an important stimulus by the recent availability of specific and sensitive methods of dosage.