Abstract: A multilumen vascular catheter for the delivery of therapeutic fluids, e.g., containing thrombolytic agents, to a patient's blood vessel. The catheter has a plurality of flow passageways in the wall of the outer tubular member in which the discharge openings thereof increase in diametrical dimensions so that a desired, e.g., uniform, flow of treatment fluid is delivered exteriorly of the catheter body. The flow passageways preferably are formed by means of lasers. A first rectangularly shaped passageway is formed in the catheter wall and then a second rectangularly shaped hole is made in the wall, overlapping the first hole to form the final rectangular shape. The catheter is particularly adapted to deliver small quantities of thrombolytic agents, such as urokinase, streptokinase, and tissue plasminogen activator.