A catheter system for localized or semi-localized administration of agents through the wall of a blood vessel is provided. Various catheter system constructions which use at least one expandable occluding device to create an isolated region are provided. Constructions using one catheter and one occlusion device are provided, along with constructions using two catheters and multiple occlusion devices. The catheter system may include a catheter with a variable stiffness along its length. The catheter system may also include a guide wire integrated with an inner catheter. The catheter can infuse the agent into the blood vessel in a pressure regulated manner. Methods for delivery and infusion of the agent within a blood vessel are also provided.