The diametral strengths of magnesia-core crowns made with different body porcelains, Will-Ceram, Crystar, Ceramco II, and Vita VMK 68, were measured. The results were compared to the diametral strengths of aluminous-core crowns and Renaissance crowns. A one-way analysis of variance showed that there were no significant differences in the strengths of magnesia-core crowns or the aluminous-core crowns, but the Renaissance crown strengths were significantly lower.