In this paper, the problem of finding a good decomposition of the manufacturing system into manufacturing cells, that can be assigned to part families is addressed. A simple twofold heuristic algorithm capable of minimizing the inter-cell material movement, and addressing industrial applications of realistic dimensions is presented. The first step of the proposed heuristic is a bottom-up aggregation procedure to minimize the "Normalized InterClass Traffic". The second step is a procedure to attempt further improvement, in which the significance of a machine to a cell is validated.