Purpose: The probability of failure under flexural load of veneered specimens of a unidirectional glass fiber–reinforced composite (FibreKor/Sculpture), a bidirectional glass fiber–reinforced composite (Vectris/Targis), a glass-infiltrated alumina (In-Ceram Alumina/Vita
), and a zirconia-reinforced glass-infiltrated alumina (In-Ceram Zirconia/Vita
) was investigated; a metal-ceramic (PG200/Vita ) system served as a control. Materials and Methods: Ten uniform beams of the veneered core materials were fabricated for each system and subjected to a three-point bending test. The data were analyzed using the Weibull method. The failure load of specimens at a 10% probability of failure (B10 load) was compared. The mode of failure was analyzed. Results: The B10 load of the systems investigated was not significantly different from that of the metalceramic system. FibreKor possessed significantly higher B10 load than Vectris, In-Ceram Alumina, and In-Ceram Zirconia. The B10 strength loads of Vectris, In-Ceram Alumina, and In-Ceram Zirconia were not significantly different from one another. Conclusion: The probability of FibreKor to fracture under a flexural load was significantly lower than that of Vectris, In-Ceram Alumina, or In-Ceram Zirconia. Int J Prosthodont 2003;16:487–492.