A catheter for use with an endoscope includes a projectable and retractable needle for the introduction of injectable drug agents and a visual-path irrigation lumen disposed adjacent to the needle for providing irrigation fluid to a target site within body tissue. The visual-path irrigation lumen enables the user in a one-catheter procedure to displace blood or other obscuring substances such that the visual path is cleared, a target injection site endoscopically identified, the needle advanced into the tissue at the site, and the injectable agent injected into the tissue.