The stability of steady‐state solutions of reaction‐advection‐diffusion equations to perturbations in the initial data is examined by means of a comparison theorem. In particular, conditions on the reactive terms and the advective terms are used to prove stability or asymptotic stability of steady boundary‐layer and shock‐layer solutions and to estimate the maximum allowable size of the initial perturbation. Many examples are discussed, including the time‐dependent Lagerstrom‐Cole problem and a problem modeling transonic flow in a no