Manufacturers generally quote indentation hardness values when predicting the clinical wear potential of newly introduced ceramic restoratives. The objective of this study was to determine whether in vitro two-body wear correlated well with hardness. A modified polisher was used to abrade enamel cylinders against polished disks of commercially available dental porcelains and glass. Enamel loss after four h was measured with a micrometer. Five ceramic materials were tested, and enamel abrasion rates were correlated with Knoop hardness values. Dicor and Dicor coated with a shading porcelain were found to cause the lowest wear of enamel. These rates were statistically significantly lower than those obtained with Optec, the most abrasive material. These findings may be due to microstructural differences between the materials. Knoop hardness showed poor correlation with the results of the abrasive testing.