This work introduces a modified MAX MIN Ant System (MMAS) designed to solve the Capacitated p-Medians Problem (CPMP). It presents the most relevant steps towards the implementation of an MMAS to solve the CPMP, including some improvements on the original MMAS algorithm, such as the use of a density model in the information heuristics and a local search adapted from the uncapacitated p-medians problem. Extensions to a recently proposed updating rule for the pheromone level, aiming at improving the MMAS ability to deal with large-scale instances, are also presented and discussed: Some simulations are performed using instances available from the literature, and well-known heuristics are employed for benchmarking. © Springer-Verlag Berlin Heidelberg 2004.3316 10941100Osman, I.H., Christofides, N., Capacitated Clustering Problems by Hybrid Simulated Annealing and Tabu Search (1994) Int. Trans. Opl. Res., 1 (3), pp. 317-336. , Pergamons Press, England, 1994Garey, M.R., Johnson, D.S., (1979) Computers and Intractability: A Guide to the Theory of NP-Completeness, , San Francisco: FreemanDorigo, M., (1992) Optimization, Learning and Natural Algorithms, , Ph.D.Thesis, Politecnico di Milano, Italy, in ItalianStützle, T., Hoos, H.H., The MAX-MIN ant system and local search for the traveling salesman problem (1997) Proceedings of the IEEE International Conference on Evolutionary Computation (ICEC'97), pp. 309-314. , T. Back, Z. Michalewicz, and X. Yao, editors, IEEE Press, Piscataway, NJ, USAStützte, T., Dorigo, M., ACO algorithms for the Quadratic Assignment Problem (1999) New Ideas in Optimization, pp. 33-50. , D. Corne, M. Dorigo, and F. Glover, editors, McGraw-HillAhmadi, S., Osman, I.H., Density based problem space search for the capacitated clustering problem (2004) Annals for Operational Research, , in pressResende, G.C.M., Werneck, F.R., On the implementation of a swap-based local search procedure for the p-median problem (2003) Proceedings of the Fifth Workshop on Algorithm Engineering and Experiments (ALENEX'O3), pp. 119-127. , Richard E. Ladner (Ed.), SIAM, PhiladelphiaTeitz, M.B., Bart, P., Heuristic Methods for Estimating the Generalized Vertex Median of a Weighted Graph (1968) Operation Research, 16 (5), pp. 955-961De França, P.O., Von Zuben, F.J., De Castro, L.N., A Max Min Ant System Applied to the Capacitated Clustering Problem (2004) IEEE International Workshop on Machine Learning for Signal Processing, , São Luis, BrazilBlum, C., Roli, A., Dorigo, M., Hc-Aco: The hyper-cube framework for Ant Colony Optimization (2001) Proceedings of MIC'2001 - Meta-heuristics International Conference, 2, pp. 399-403. , Porto, PortugalBlum, C., Dorigo, M., The Hyper-Cube Framework for Ant Colony Optimization (2004) IEEE Transactions on Systems, Man and Cybernetics, Part B, 34 (2), pp. 1161-1172Lorena, L.A.N., Senne, E.L.F., Local Search Heuristics for Capacitated P-Median Problems (2003) Networks and Spatial Economics, 3, pp. 407-419