A comparison of the drying efficacy of ambient-air drying of large forage bales was made between positive and negative pressure systems. Both systems effectively dried the bales to the desired average moisture content, but regions of higher moisture content within the bales were measured with the two systems. Energy consumption as expressed as the ratio of the energy consumed/weight of moisture removed was similar for both drying systems. Final configuration of the drying system will depend on whether heat is required to speed the drying process in order to meet the capacity of the harvesting system.