Complications of intra-arterial chemo-infusion therapy using a implantable vascular access system (VAS) were summarized in this paper. Nine patients with hepatic metastases of colorectal cancer received continuous 5-fluorouracil (5-FU) infusion into the gastroduodenal artery. Sixteen patients with breast cancer were administered epi-adriamycin (Epi-ADM) singly or in a combination of 5-FU and mitomycin C through both subclavicular artery and internal thoracic artery. One case with liver metastases showed gross necrosis of anterior section in the liver caused by continuous infusion of 5-FU. Troubles associated with VAS included obstruction of VAS in 3 patients, bleeding or leakage of drug caused by injured port of VAS in 3 patients, and localized subcutaneous infection was observed in one patient. Complications caused by carelessness of doctors occurred in two patients. Since damage of VAS was observed frequently, we performed a pressure test for VAS. Saline was injected at various pressures into the port connected with the obstructed catheter. All samples tested showed neither damage nor leakage under 75 psi. After 20 punctures in a narrow area of 5 mm in diameter, however, one of eight samples showed leakage of saline from the septum in 50 psi. A syringe of 1 ml was found to produce over 10 times higher pressure than that of 10 ml when compressed by the same force, because the cross section of a 1 ml syringe is about 9% that of a 10 ml syringe. In conclusion, to prevent undesirable complications a better education and understanding of implantable VAS are necessary.