Objective: To evaluate the ability of a two-phase calcium-containing sodium bicarbonate-based toothpaste to mineralize the surface of enamel . Methods: Etched enamel specimens were prepared by drilling 3-mm (nominal) cores from human molars. After being mounted and masked, they were polished with 800- and 1200-grit diamond paper, and etched by 70 minutes exposure to an acidic soft drink. Scanning electron microscopy (SEM) images were taken of enamel surface sites before treatment. The test products were (1) a two-phase toothpaste (T-1) containing calcium, fluoride, and phosphate ions, together with sodium bicarbonate and (2) a conventional sodium fluoride/silica product (C-1) (Crest® Cavity Protection Regular). Three specimens for each product were exposed 20 times, for five minutes each, to a 1:2 slurry of toothpaste in water, followed by a 1-min wash with apatite-saturated water. The imaged sites were then relocated and reassessed by SEM. Results: SEM pictures show T-1 deposits new mineral on the eroded surfaces of the prisms, so that their boundaries become obscured and the surfaces become smoothed. In contrast C-2 leaves the surfaces essentially unaltered. . Conclusion: The calcium-containing, two-phase sodium bicarbonate toothpaste can mineralize the surface of etched enamel and smooth the surface.