The problem of allocating non-identical machines among non-identical servers is considered under steady-state conditions for the case of quasirandom input and exponential service times. Machines are assigned to operators with the objective of minimizing an expected cost model of the queueing system. Different classes of machines have different service rotes and, for a given class of machines, the service rates are different among servers. A pattern search procedure is used to solve the resulting optimization problem. Computational experience is presented, together with an analysis of the sensitivity of the model to errors in estimating the values of the parameters of the model.