In today's competitive manufacturing environment, companies are constantly looking for ways to improve. Because of this, many companies are striving to become "lean" by implementing lean manufacturing, which is a difficult process. To aid in the implementation of lean manufacturing, simulation was used to reduce the trial-and-error period of lean manufacturing and find to optimum approach to implement the lean manufacturing principle. In this research, a case study of implementing level loading of the production schedule for BullFrog International, L.C. will be examined. To make it possible to implement level loading, the thermo-former machine at the beginning of the operations was improved to allow quick changeovers. The changeover time was reduced by 60% and with a few additional changes changeovers could be completely external. In order to be able to conduct simulation experiments to find the optimum production schedule, cycle times were gathered for each operation and a simulation model was developed of BullFrog International, L.C. current manufacturing operations. Historical data was gathered of previous month's sales orders and orders were divided into three different groups. Group 1 the spa orders are roughly 50% single-pump and 50% double-pump, group 2 the spa orders are roughly 60% or more single-pump spas and group 3 the spa orders are roughly 60% or more double-pump spas. Using historical data, level loading production schedules were developed using lean manufacturing principles by reducing lot sizes to the smallest possible and still preserving the correct ratios. All of these suggested production schedules were tested with the simulation model and through various experiments, the optimum production schedule were determined. The optimum production schedules were implemented and the results were recorded. The results were an average throughput increase of 49.1% in group 1, an average throughput increase of 58.7% in group 2 and an average throughput increase of 58.7% in group 3. These results support the hypothesis that level loading will increase throughput in a complex manufacturing system where there is a high mix and low volume production schedule. The results also support the hypothesis that the trial-and-error period was reduced by the use of simulation.