The thermal shock behavior of an alumina monolith and two alumina-iron ceramic-matrix composites has been investigated by superimposing the measured K-R-curves of the materials onto the theoretically generated curves of the thermally induced stress intensity factor. Predictions of the critical-temperature differentials and retained strengths after quenching are in good agreement with the experimental data. The inclusion of metallic particles into an alumina matrix improves the thermal shock resistance, although the increase in toughness is not solely responsible for this improvement. There is a decrease in thermal stress-intensity factor that is generated for the composites; this decrease is due to a reduction in the Young's modulus and/or Plot modulus. However, the increased toughness for large crack lengths may offer increased damage resistance for severe thermal shock treatments.