This Note analyzes the availability of supervised protective systems for nuclear reactors. Failure and repair times are assumed to be exponentially distributed. The availability is maximized, subject to a given fixed amount of resources, by determining the optimum distribution of resources between supervision and repair facilities and by selecting the optimum active-inactive times of the supervisor. The mathematical formulation employs a Markov model continuous in time and alternating between two and three discrete states. Maximization of availability is achieved by using a modified pattern search technique. Computer results illustrate the usefulness of the approach.