Constructional details are given of a complete Geiger‐Mu¨ller counting system consisting of a stabilized high voltage supply, Neher‐Harper coupling circuit and vacuum‐tube scale‐of‐eight feeding a Cenco counter stage. The system is entirely a.c. operated. Its resolution time of 6.5×10−6second allows it to follow the G‐M circuit without counting losses. The counting losses in the Cenco counter stage are negligible for random input rates to the system up to 20,000–30,000 counts a minute.