Diluting composite materials with unfilled resin to facilitate clinical application during direct lamination will result in an alteration of filler loading with possible changes of physical properties. This study compared the surface hardness and abrasion resistance of a visible light-cured microfilled and hybrid resin with and without dilution. Samples were prepared, cured, and stored in distilled water at 37 degrees C for 24 hours before testing. Knoop hardness values were obtained from the upper surface of 10 samples in three dilution and control groups of each material. Three samples of the dilution and control groups were similarly prepared and stored for toothbrush abrasion testing. Data from the hardness and abrasion tests were subjected to analysis of variance and Tukey's test at a 0.05 level of significance. Results showed that dilution had a significant effect on surface hardness of the materials tested, although the diluted materials were not significantly different from the controls. Abrasion tests showed visible evidence of abrasion on all samples, but dilution showed no significant effect on abrasion resistance of the materials tested.