The interest of patients in vital tooth bleaching has created a demand for treatment. However, few objective data are available to help determine the number of bleaching appointments necessary and the lightening that can be expected. The purpose of this study was to measure color changes in bleached extracted teeth and compare these to control groups. Group A was etched and bleached with 35% stabilized hydrogen peroxide. Group B was treated the same as group A, but the bleaching solution was replaced with distilled water. Group C was not treated, but was stored in water. Mean color difference after one treatment was 3.33 for group A, 1.67 for group B, and 0.48 fo r group C. After six treatments, the overall color difference was 3.82, 2.41, and 1.38 for groups A, B, and C, respectively (P .01). Color changes beyond those found after the first treatment were small, suggesting that there was little benefit in repeated bleachings under the conditions of this study.