Aprotinin is an important member of a family of related protease inhibitors and has many clinically beneficial activities. These inhibitors have multiple functions, but not all of them are mediated by enzyme inhibition. Aprotinin has complex effects on many homeostatic functions including coagulation, platelet function and inflammation. It also has complex interactions with other drug therapies including angiotensinconverting enzyme inhibitors. Since patients with cardiovascular diseases are treated frequently with angiotensin-converting enzyme inhibitors and also often need cardiopulmonary bypass surgery and receive aprotinin, these interactions are potentially significant but often overlooked. Aprotinin is currently used to reduce the amount of transfused homologous blood (during cardiopulmonary bypass surgery) and thus, the risks associated with homologous blood transfusion. Aprotinin also has potential uses in acute pancreatitis, carcinoid tumors, sepsis, and other clinical situations. Future research will provide a definitive answer for the need to employ this inhibitor therapeutically in these situations. Aprotinin also has some potentially adverse effects in the kidney in special circumstances. For example, the use of aprotinin in diabetic patients may be related with an increased risk for renal dysfunction. It has also been associated with thrombosis, inadequate coagulation, and allergic reactions. In balance, the available information indicates that the advantages of its application outweigh its disadvantages in most patients.