The purpose of this study was to determine the effects of four 10% carbamide peroxide gels on surface roughness (profilometer), lightness (colorimeter) and hardness (Rockwell) of three composite resin materials. Twenty samples of each composite resin were prepared and treated every 2 hours with fresh carbamide peroxide gel for 14 days. Only two groups had a statistically significant increase in surface roughness: Prisma APH with White & Brite and Silux Plus with Gly-Oxide. Three groups had a statis tically significant increase in lightness: Prisma APH with Gly-Oxide, Bis-Fil with Proxigel, and Bis-Fil with Gly-Oxide. Four groups had a statistically significant increase in hardness: Bis-Fil with Lighten, Bis-Fil with White & Brite, Prisma APH with White & Brite, and Prisma APH with Gly-Oxide. All these effects were minimal and probably not clinically significant.