Summary: We consider a single capacitated facility dedicated to the manufacturing of a set of sub-assemblies in a just-in-time (JIT) environment. The items processed on this bottleneck facility flow to a downstream assembly facility, where they are assembled according to a specified mix. We develop a simple and efficient lot-scheduling heuristic that generates feasible and least-cost manufacturing schedules for the bottleneck facility. Our heuristic was shown, through an extensive empirical comparison, to have significant advantages over an earlier proposed heuristic in the JIT literature in terms of cost performance and computational efficiency. Moreover, the results of the comparison revealed that our heuristic is more consistent with JIT objectives since it tends to generate manufacturing schedules with shorter production cycle times and fewer assemblies.