Purpose: This study determined the fracture strength of magnesia-core porcelain after using a glass infiltration firing technique. Materials and Methods: Eighty refractory dies were replicated from a stainless steel master die milled to the dimensions of a maxillary premolar that had been prepared for a porcelain crown. The core porcelain was applied to the refractory dies using traditional condensation methods, and then formed into standardized copings using a centrifugal sculpturing device. The copings were vacuum-fired from 593 degrees C to 1 of 8 high temperatures. Five copings per temperature were then coated with a glass-infiltrate and ground back to a standard t hickness. The finished copings were bonded to a duplicate die with an adhesive resin luting system and placed in an Instron testing machine and loaded to fracture. Results: Analysis of variance and Student-Newman-Keuls tests demonstrated significant differences among treatments and temperatures (P < 0.05). A significant increase in fracture strength was observed after glass infiltration of the magnesia-core porcelain. Sintering the copings to 871 degrees C or 899 degrees C prior to glass infiltration gave the highest fracture load values. Conclusion: Glass infiltration significantly increased the fracture strength of the magnesia-core porcelain.