Given a stabilizable linear system Ex/spl dot/ = Ax + Bu with sE - A regular, we analyze the stability robustness of the closed-loop system (E + BK) = (A + BF)x + v, obtained by proportional and derivative (PD) state feedback u = Fx Kx/spl dot/ + v. Our goal is to maximize the stability radius of the closed-loop system matrix s(E + BK) - (A + BF) over all stabilizing PD state feedback control laws. This problem turns out to be equivalent to a particular H/sup /spl infin//control problem for a generalized state-space system and reduces to a system of matrix inequalities. Under certain conditions the problem actually reduces to an LMI system. We also show how to apply these ideas to higher order dynamical systems.