This paper presents a scheduling approach, based on Genetic Algorithms(GA), developed to address the scheduling problem in manufacturing systems constrained by both machines and workers. The GA algorithm utilizes a new chromosome representatioiz, which takes into account machine and worker assignments to jobs. A study was conducted, using the proposed scheduling method, to compare the performance of six dispatching rules with respect to eight performance measures for two different shop characteristics: i ) dual-resources (machines and workers) constrained shop, and ii) single-resource constrained shop (machines only). An example is used for illustration. The results indicate that the dispatching rule which works best for a single-resource constrained shop is not necessarily the best rule for a dual-resources constrained system. Furthermore, it is shown that the most suitable dispatching rule depends' on the selected performance criteria and the characteristics of the manufacturing system. Notations 1. INTRODUCTION 1 k I t Ji Di Mi wk Ti Oij ' ij Sij Cij tijk =The ith job (i = I , 2, .., n) = The kth machine (k = I , 2, .., m) = The Ith worker l(1 = I , 2, .., p) = Time = Number of operations of Job i = Batch size of part i (i = I , 2, .., n) = Machine index = Worker index = Processing time of each part (sum of processing times of each operation) = Operation number j ofjob i = Ready time of operation j ofjob i = Starting time of operation 0, = Completion time of operation 0, = Processing time of operation 0, on = Efficiency of worker I on machine k = Due date ofjob i ( i = 1,2, .., n) = Utilization of machine k ( k = 1,2, .., m) = Utilization of worker 1 ( I = I ,2, .., p) = Release time of machine k = Release time of worker 1 machine k