Stable controllers are required due to modelling imperfections and for better performance achievements. As is well known, a stable stabilizing controller for a given real-rational plant exists if and only if the plant staisfies the so-called parity interlacing property. In this paper, a recent result, which proves that this condition is also necessary for infinite-dimensional plants is first presented. The condition is also sufficient if the plant satisfies certain additional properties. This result is then applied to time-delay systems. Two examples are considered. For the first example it is shown that it is not possible to design a stable stabilizing controller. For the second example it is shown that there exists a stable controller which stabilizes the plant and the design of such a controller is demonstrated. © 2012 IFAC.