H-infinity-output feedback control is applied to the control of automobile active suspensions based on a dynamic model of the full vehicle. The output feedback control is desirable from the viewpoint of implementation in the sense that it reduces the number of measurements drastically compared with state feedback used currently in suspension control. In this paper, the authors show that a linearized moder can be block-decoupled by a similarity transformation, which reduces the controller complexity significantly. The uncertainties of the vehicle model rue properly taken into account in the derivation of the Hm controller. The controller is actually Implemented in a commercial car, and the performance is evaluated both by simulations and experiments. The performance obtained proves to be quite satisfactory.