In this study, a novel intravascular drug delivery system was developed in which a drug injected from a catheter was fixed to the vasculature of the targeted tissue. Cellular proteins of viable endothelial cells were first biotinylated directly by biotinylation reagents, and then bound by an avidinated drug or, using avidin as a linker, a biotinylated drug. In the initial experiments, we studied in vitro the biotinylation of cultured bovine aortic endothelial cells (BAECs) by applying biotinylation reagents (NHS-LC-biotin or sulfo-NHS-LC-biotin) onto the washed intact BAEC monolayers and showed that the amount of biotin bound to the cells depended on the concentration of the biotinylation reagents applied. The cell-bound biotin decreased with time after the biotinylation. When fluorescein-labeled avidin (FITC-avidin) was applied to the biotinylated BAEC monolayers, the FITC-avidin readily bound to the cells. An LDH-release assay showed that sulfo-NHS-LC-biotin was only slightly cytotoxic to the BAECs and a colony formation assay showed only slight adverse effects of the reagent. In vivo studies were carried out on the renal arteries of normal rabbits. A solution of NHS-LC-biotin was injected through a catheter to one kidney to biotinylate its vasculature and the vehicle to the other as control, followed by a perfusion with saline. Finally, a solution of FITC-avidin was injected to both kidneys that were then reperfused with the blood flow following the withdrawal of the catheters. In the histological sections, more than 85% of glomeruli was stained with fluorescein in the biotinylated kidney, whereas no glomeruli were stained in the control. In the kidneys harvested 2 days after the same procedure, most glomeruli were still brightly stained. In the final experiment, biotinylated kidneys were injected with a solution of avidin, followed by a solution of fluorescein-biotin. Control kidneys had no prior biotinylation but received the same injections of avidin and fluorescein-biotin as above. More than 80% of glomeruli were stained in the biotinylated kidneys but none in the controls. This indicated that biotinylated drugs can be anchored to the biotinylated vasculature through avidin without being flushed away by blood flows. No apparent adverse effect was found in the functions of biotinylated kidneys. We propose that this drug delivery system is feasible for the treatment of some pathological conditions of blood vessels such as microvascular proliferation in malignant tumors and for continuous drug delivery in certain target organs.