Abstract: Methods and devices are disclosed for selective delivery of therapeutic substances to specific histologic or microanatomic areas of organs. Introduction of the therapeutic substance into a hollow organ space (such as an hepatobiliary duct or the gallbladder lumen) at a controlled pressure, volume or rate allows the substance to reach a predetermined cellular layer (such as the ephithelium or sub-epithelial space). The volume or flow rate of the substance can be controlled so that the intralumenal pressure reaches a predetermined threshold level beyond which subsequent subepithelial delivery of the substance occurs. Alternatively, a lower pressure is selected that does not exceed the threshold level, so that delivery occurs substantially only to the epithelial layer. Such site specific delivery of therapeutic agents permits localized delivery of substances (for example to the interstitial tissue of an organ) in concentrations that may otherwise produce systemic toxicity.