The implantation of a small silicon catheter for repeated intravenous applications of drugs in laboratory animals (rats) is described. Under an operation-microscope, the catheter is inserted into the external jugular vein and remains in situ in a skin pocket during the treatment. By dissecting the wound, multiple fractions of drugs can be administered via the catheter at intervals of days or weeks. The method has the advantage that in long-term studies with rats, intravenous injections or infusions of cytostatic drugs are possible with high accuracy.