The radial servo system of a compact disc player has to cope with large gain variations which are due to disc dependent optical characteristics, tolerances in mechanical and electrical components and nonlinearity in the generation of the position index. In current players this problem has been solved by using an adaptive control scheme based on an injected signal to identify the process gain. This paper discusses the application of the general Self Tuning Regulator (STR) concept to the control problem of the radial servo system. The STR principle depends on parametric identification and control adaptation without additional excitation of the control loop. The concept has been implemented in an experimental arrangement; it gives good control performance and is insensitive to practical perturbations.