Asymptotic formulas are derived for the partition function of multichain closed product form networks with groups of stations, each group consisting of many identical stations. The derivation of the asymptotic expansion is based on an integral representation of the partition function in a multidimensional complex space and its evaluation using the saddle point method. The saddle point method is also used to derive an iterative algorithm which reduces the problem of solving the multichain network to a set of single chain problems. The accuracy of the approximations is evaluated in two case studies: a memory interference model in a multiprocessing system and a model of a multiprogramming system. © 1992, Taylor & Francis Group, LLC. All rights reserved.