Porous fused silica ceramics which had been partially devitrified to cristobalite were stronger at 350 degrees C in the beta-cristobalite stability range, but weaker at 25 degrees C after the transformation to alpha-cristobalite. The tensile strength distribution for different cristobalite fractions are compared for three types of specimens. These were beta-cristobalite samples which had never been transformed to alpha-cristobalite; room-temperature samples with alpha-cristobalite; and samples at 350 degrees C which had retransformed to beta-cristobalite after prior transformation to alpha-cristobalite. The alpha-cristobalite samples displayed 50%-75% the strength of samples tested on beta and the difference in strength was dependent on cristobalite content. Specimens retransformed to beta-cristobalite had strength similar to virgin specimens. Microcracking associated with the transformation to alpha-cristobalite contributes to the strength changes but cannot fully explain the impact of the beta-alpha transformation on strength.