Mechanical and heat treatment characteristics of two nickel-chromium-based dental casting alloys were investigated. Both alloys showed rapid response to heat treatment. In their softened state the alloys lost 25 to 50% of their as-cast hardness. Elongation was 20 to 45%. Rehardening nearly restored as-cast strength, whereas elongation values remained at 10 to 17%.In recent years base metal alloys have almost replaced gold in the fabrication of large dental appliances and have made inroads with the smaller castings through the porcelain-fused-to-metal restoration. The main problems with the base metal alloys can be associated with their excessive hardness and inadequate elongation. Modification of the properties of cobalt-chromiumand of cobalt-nickel-chromium-based alloys through heat treatment, compositional alterations, and variations in investing and casting techniques have been described by other authors.1-8 Little information is available, however, regarding the properties of the newer nickel-chromium-based casting alloys.The purpose of this study was to investigate heat treatment effects on the mechanical properties of two commercial nickelchromium-based alloys,* to define critical treatment parameters such as heat treatment temperature and time, and to suggest practical application of the experimental results.