The effects of four bleaching agents (Opalescence, hiLite, 30% hydrogen peroxide, and 30% hydrogen peroxide mixed with sodium perborate) and 37% phosphoric acid on the external surface of human enamel were examined with the scanning electron microscope. The materials were applied to the enamel surfaces of 60 specimens obtained from 10 teeth. Each test agent was applied to one specimen from each tooth. One specimen of each tooth was left untreated. Comparison to the untreated control surfaces revealed that enamel exposed to the bleaching agents underwent slight morphologic surface alterations. The enamel surfaces treated with phosphoric acid, in contrast, showed severe morphologic alterations.