Increasing shop floor efficiency has always been a major concern of manufacturing companies. Scheduling applications have been successfully employed to create optimized plans which manufacturers can use to run their operations. But it is a common occurrence in today''s dynamic manufacturing environment that the information upon which a schedule is based often changes after the schedule has been created. Running shop floor operations based this out of date information can lead to increased shop floor inefficiency. Systems need to be developed which not only provide good initial schedules, but also can react to changes in the state of operations of the shop floor by producing and executing updated schedules. Research is underway at the National Institute of Standards and Technology(NIST) to develop standards and procedures which facilitate the development of reactive scheduling systems. A reactive scheduling system is one that not only produces initial schedules for production, but also: 1)monitors the shop floor events and evaluates compliance to the schedule and other shop floor performance related criteria; 2)collects shop floor status information to enable the creation of updated schedules based on current information; and 3)produces new schedules based on the collected information and incorporates the new schedule information into the current shop floor operations. A key area of research in developing this approach is the use of a discrete event simulation system as proxy for a real shop floor and shop floor data collection system. A prototype is being developed at NIST which uses simulation as proxy for a real shop floor and shop floor data collection system. The use of simulation enhances the ability to do this research by: 1)greatly reducing the cost because a real shop floor is not required; and 1)greatly increasing the number of shop floor configurations that can be examined. In this paper the changes that were made to the simulation system to incorporate it into the reactive scheduling system prototype will be discussed.