In this paper we present a study of an Ant Colony System (ACS) for the two-dimensional strip packing problem. In our computational study, we emphasize the influence of incorporating a simple optimization method at each cycle of the ACS. In this hybrid approach, local optimization is applied to a subset of the newly generated solutions to move them to a local optimum. We show that our ACS algorithm, when combined with a fine-tuned local search procedure, can compete with an existing genetic algorithm, reaching solutions of good quality and also exhibiting low execution times.