Because of the special anatomical conditions of neurosurgery, the success of any operation depends on accurate haemostasis. This paper reports on an additional measure for the achievement of intraoperative haemostasis which has been successfully used during more than 1200 neurosurgical interventions. Meninges and cerebral tissue contain relatively high concentrations of tissue activators of plasminogen. As a consequence, a stable wound closure by fibrin is generally impaired during neurosurgical operations (1, 5, 6). Aprotinin, a polypeptide obtained from bovine organs, is a potent inhibitor of plasmin which inactivates the free enzyme by forming a very stable complex (7). By competitive inhibition, aprotinin is able to act as selectively on physiological fibrinolysis as the naturally occurring inhibitor c~2-antiplasmin. At very high local concentrations of the inhibitor hardly any plasmin is available for the splitting up of fibrin. On the other hand, this inhibition of fibrinolysis is reversible when the local inhibitor concentration declines, since both the availability of plasminogen and its activation are not affected. This is an important difference compared with the mode of action of synthetic antifibrinolytics such as tranexamic acid*. A fibrin-stabilising effect by high local concentrations of aprotinin is routinely produced when the fibrin-glue technique is used (3). A comparable effect can be achieved by the topical intraoperative application of a commercial aprotinin solution**. The sterile solution is isotonic and has a pH of 6-7. It contains 20,000 KIU (Kallikrein Inactivator Units) per ml and is available in ampoules of 5 and 10 ml. The solution is applied by impregnating haemostatic dressings (swabs) of fibrin foam. In addition, up to 10 ml of Trasylol is instilled into the