A vacuum system leak detection technique (Reverse Flow Leak Detection) under development at Teledyne Brown Engineering in Huntsville, AL. for use aboard Space Station Freedom is presented. The technique will be applied to the Vacuum System (VS) and Waste Gas Management Subsystem (WGMS) of the U.S. Lab Module. These two systems contain over 45.7 m. of distributed vacuum tubing located in remote utility runs. Fluid flow calculations which utilize known system geometry and measured steady state pressure measurements from the VS and WGMS can be used to identify leak sites within ±38 cm. Exact leak position can then be pinpointed by conventional tracer gas leak detection in the identified region. Tests have been performed using a simple, unrestricted 12.8 m length of vacuum tubing with a calibrated air leak attached. The 12.8 m tube is alternately evacuated by cryopumps on either end. Steady-state pressure measurements taken before and after flow reversal in the system have been used to locate leaks accurately.