Abstract: The invention relates to a probe for treating varicose veins, comprising a flexible plastic tube with a tip portion which can be guided through varicose veins at its front end, the tube being at least as long as the veins to be treated. To enable a sclerosing agent to be injected at desired points along the varicose vein, the invention proposes that the probe should have at least one lateral opening in the region of the tip portion, and that the inner cavity of the tube should form a flow connection from a joining piece at the rear end of the tube to the lateral opening, for injection of sclerosing agent.