Purpose: To evaluate the effect of casein phosphopeptide-amorphous calcium phosphate (CCP-ACP) application on the microhardness of bleached enamel and compare it to that of fluoride application. Methods: 10 extracted bovine incisors were cut into four sections (4 x 4 x 3 mm) that were randomly distributed among five groups (n=8). All groups were bleached three times using 38% hydrogen peroxide (HP), with 5-day intervals between bleaching, according to the following treatment protocols: Group A: bleaching only; Group B: bleaching + daily CCP-ACP paste; Group C: bleaching + daily casein phosphopeptide-amorphous calcium fluoride phosphate (CPP-ACPF) paste; Group D: bleaching + daily 250ppm NaF solution; Group E: bleaching + APF gel (once after final bleaching). Specimens were maintained in artificial saliva throughout the experiment. Baseline and post-treatment Vickers microhardness values were obtained for all specimens. Statistical analysis was performed using one-way ANOVA and post-hoc Tukey tests. Results: Groups B and C showed significant increases in enamel microhardness following treatment (P< 0.001), whereas no statistically significant changes were observed in Groups A, D, or E (P> 0.05). One-way ANOVA of Delta Vickers microhardness numbers (Delta VHN) revealed significant differences among groups (P< 0.001), with Group B showing the highest Delta VHN and Group A the lowest. (Am J Dent 2009;22:393-396).