A method and device for determining the hydraulic leakage rate of liquid-conveying parts, in particular injection valves for internal combustion engines, place the liquid-conveying part into a test body, and the liquid-conveying part is charged with a test liquid under a particular pressure, and a carrier gas stream is provided in a flow duct of the test body, and a vapor mixture behind the liquid-conveying part is conducted to an analyzer, and a measurement and analysis are carried out, using the analyzer, of the hydraulic leakage rate of the liquid-conveying part via the concentration of test liquid in the vapor mixture, the carrier gas stream being brought in via a nozzle element close to the leakage point of the liquid-conveying part, and/or a heating of the vapor mixture being provided behind the liquid-conveying part for complete conversion into the gas phase. The testing device is particularly suitable for leakage measurement in fuel injection valves used in fuel injection systems of mixture-compressing externally ignited internal combustion engines.