An active control technology has been developed and applied to a broad class of vibration isolation problems in order to improve the riding quality and running stability of ground vehicles. The performance of an active secondary suspension applied to a high-speed magnetically levitated vehicle running on a rough guideway is analyzed for both a small and a full-sized vehicle. The small model is analyzed theoretically and experimentally, using in the latter case a laboratory-scale suspension equipped with a microcomputer-controlled pneumatic actuator. The large model is examined by computer simulation. The results are discussed with reference to a performance index reflecting passenger comfort.