Describes the application of the HERS BESTEST system to a building energy simulation computer program. There was good agreement between the simulation computer program predictions and those of the reference programs. Different simulation inputs can be the cause of major differences between program predictions. The authors recommended that the HERS BESTEST manual be modified to include detailed information about the house models used to generate the results with the reference software tools. Indications were alos that the HERS BESTEST can be an effective means of diagnosing potential problems with simulation software.