This work combines local search with a variant of the Ant System recently proposed for partitioning problems with cardinality constraints. The Coloured Ant System replaces the classical concept of trail with p trails of different “colours”, representing the assignment of an element to one of the classes in the partition. We apply the method with promising results to the design of local telecommunication networks. The combination of the Coloured Ant System with local search yields much better results than the two approaches alone.