Abstract: The present invention relates to a pitch control system for operating the blade pitch of the rotor blades of a wind turbine generator. A method is disclosed wherein a command signal or pitch demand is applied to the blade pitch system of the rotor blades and the resulting response signal or pitch response is received. The received pitch response is compared to a reference and a signal indicative of a pitch system fault may be generated if a difference between the response signal and the reference is detected as being larger than a preset criterion. The deviating behaviour of a blade pitch system can thereby be detected which enables a testing or monitoring of the condition of the pitch system of the rotor blades of a wind turbine generator.