A dynamic fatigue indentation technique was used to determine the slow crack growth (SCG) parameters of a medical-grade platelet-reinforced zirconia-toughened alumina and two different fine-grain aluminas: one a common grade of nominal 99.5% purity, and the other a high-purity (99.94%) medical-grade alumina. Fatigue tests in bending were performed at various loading rates with precracked Vickers indentations in 100% relative humidity conditions. Inert strength tests were performed in dry nitrogen. The dynamic fatigue analysis accounts for the presence of the indentation. The SCG power law exponent was found to be 36, 65, and 93 for the 99.5% alumina, the 99.94% alumina, and the zirconia-toughened alumina, respectively. The presence of glassy phase likely increases SCG in the 99.5% alumina compared with the higher purity alumina. The zirconia-toughened alumina exhibits a relatively steep R curve that forms due to two toughening mechanisms: platelet reinforcement and transformation toughening. It is apparent that neither of mechanisms degrades significantly due to moisture-assisted SCG.