A reflectionless termination design is described which, in principle, can be adapted to wave‐guide or coaxial transmission lines. Reflection coefficients of 0.001 were obtained experimentally withX‐band wave‐guide terminations. The termination comprises a section of transmission line into which is fitted a tunable sliding load. The sliding load is tuned to be reflectionless by means of the ``sliding load'' method of measuring reflection coefficients. The termination can be operated over a wide frequency range but must be retuned each time the frequency is changed.The wave‐guide circuit of the load is analyzed and design equations are derived.The reflectionless wave‐guide termination is primarily useful as a reference standard for microwave impedance bridges.