Intravascular catheterization is a very common method of drug administration. Proper utilization of catheters requires knowledge of the physio-chemistry of the drugs in solution, the relevant pharmacokinetics of drug disposition, and in some instances the fluid mechanical events that occur as solutions are infused into the blood stream. For example, intra-arterial chemotherapy offers an alternative to systemic (iv) chemotherapy for localized neoplasms. Infusion of chemotherapeutic agents directly into the arterial supply of a tumor can allow high local drug concentrations in the tumor-bearing tissue while minimizing systemic toxicity. Application of this procedure in patients has produced varied results. For example, intracarotid infusions of cisplatin and BCNU have shown some evidence of regression of glioblastomas, but have also resulted in frequent episodes of leukoencephalopathies and other focal lesions, such as ophthalmic toxicity. These findings suggest the influence of streaming of the drug solutions from the catheter tip and inadequate mixing and distribution to distal tissue regions. This hypothesis was verified in an in-vitro flow model of the human carotid artery system. The results of dye injection studies indicated that streaming is likely to occur during low infusion rates, and that mixing can be enhanced by increasing infusion velocities, by improving catheter tip design, and also by modifying the mode of injection such as infusing transverse or retrograde to the blood flow.