Considerable gains in the performance of a wave energy device are possible when the power take-off mechanism is able to control the hydrodynamic response of the device. This paper reports work on the practical realization of such a mechanism for the oscillating water column device. The servomechanism and the analogue control circuit were tested in the laboratory for a number of regular wave frequencies. The results demonstrate that an oscillating water column of given dimensions can be made to resonate at any chosen frequency of interest by controlling the phase of the load acting on it. A short description of the system is presented together with the tests performed, and the results are discussed in detail.