We consider robust stabilization of linear MIMO systems, whose physical parameters are allowed to deviate from the nominal ones within known bounds, and the control plant is subjected to unknown power-bounded polyharmonic external disturbances (with unknown amplitudes and frequencies). The problem is to design a robustly stabilizing controller such that the prespecified errors for the controlled variables in steady state are guaranteed. The solution is based on the “loop-breaking technique” of the plant-controller system with respect to the physical parameters, e.g. Chestnov (1999); it reduces to the standard H_infty-optimization procedure by properly choosing the weighting matrix at the controlled variables. This approach is implemented numerically in the MATLAB-based Robust Control Toolbox (RCT).