An experimental investigation into model reference adaptive control of an electro-hydraulic servo-mechanism is reported. The servo-system consisted of a zero-lapped servo-valve and asymmetric actuator positioning a load of 890 kg. Parallel model reference adaptive control was employed with the desired level of system performance being specified in terms of a reference model transfer function. The performance of the basic scheme is enhanced by the introduction of a novel integral-action controller and typical performance characteristics with and without the controller are presented. The ability of the adaptive controller to maintain a consistent level of performance when subjected to a pseudo-random control signal is also discussed.