This paper considers a linear time invariant lumped multivariable feedback system consisting of a plant, which is subjected to perturbations, a precompensator and a feedback compensator. Given that, the nominal feedback system is exponentially stable and achieves considerable disturbance rejection, this paper establishesnecessary and sufficientconditions on thenominalfeedback system so that, over the prescribed class of additive/multiplicative perturbations, all perturbed feedback systems preserve stability and considerable disturbance rejection. The generalization to distributed systems and the extension to discrete systems are indicated.