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This paper outlines a new method of measuring the dynamic characteristics of gas regulators, which has been developed recently at the British Gas Corporation's Engineering Research Station (ERS). The method has the advantage of not requiring fast acting control valves as part of the test equipment, and the results obtained are not confused by test pipework effects, a problem with other methods. Furthermore, all common test methods can be used, including frequency response and stochastic, as well as the step tests in wide use at present. The new technique injects disturbance pressures into a closed-loop regulator, by means of a ‘pressure servo’ fitted into its sense line, and then measures those disturbances as they progress through various regulator components, such as the controller. The new method can be applied to regulators with deformable control elements as a way has been developed of directly measuring instantaneous gas sizing coefficients at frequencies up to 12 Hz without using position indicators. The test principle may have application in the dynamic testing of other regulation systems, such as electrical power supplies and heating equipment.