Dental ceramics generally fail because of the growth of microscopic surface flaws that form during processing or finishing or that result from surface impact during service. The ion-exchange process has been shown to be effective in improving the flexural strength of most dental porcelains through the development of a compressive surface layer. The Vickers hardness and crack resistance of several commercial dental ceramics were determined by indentation techniques. The results of this investigation indicate that ion-exchange reinforcement can significantly improve the resistance of the ceramic surface to crack propagation with little effect on apparent surface hardness.