The main purpose of this laboratory study was to determine the tooth whitening effect of a baking soda dentifrice containing stabilized 1% hydrogen peroxide following repeated applications to intrinsically stained teeth. Additional objectives were to investigate (1) the influence of tooth surface curvature and moisture on color measurements, (2) preliminary treatment parameters using 1% hydrogen peroxide solution, and (3) the relationship between Vita shade guide standards and instrumental color readings. Human tooth specimens with intrinsic stain were specially prepared and measured for color (L*a*b*) by means of diffuse reflectance spectrophotometry. Specimens were measured under wet and dry conditions with natural and flattened enamel surfaces. A preliminary test was conducted with 1% H2O2 solution to establish tooth whitening versus treatment time. Then, new tooth specimens were treated repeatedly with slurries of silica, baking soda, or baking soda/peroxide dentifrices at 30-minute intervals, and color measurements were taken under both wet and dry conditions after 4, 8, 16 and 24 hours. L*a*b* color measurements of the Vita shade guide teeth were also made in order to relate laboratory color changes to clinical effects. The parameter testing results showed that flattening the enamel surface had no effect on tooth color, but the teeth rapidly became lighter and less yellow upon air-drying. The 1% H2O2 solution caused both a significant decrease in yellow (b*) and an increase in lightness (L*). Since the reduction for b* occurred more rapidly and to a greater extent than the L* factor, the b* component may be the more important indicator of tooth whitening by bleaching. Compared to the silica and baking soda dentifrices, the baking soda/peroxide dentifrice significantly decreased the yellow color (b*) of the teeth after 8 or more hours of topical treatment. The instrumental color readings of the Vita Shade guide teeth showed that the color differences between the standards were not linear or consistent, and their accuracy for assessing clinical changes in tooth whiteness is questionable.