Many clinicians advocate etching the teeth before vital bleaching as a way to enhance the permeability of the tooth surface to hydrogen peroxide and thus to enhance the bleaching effect. However, no studies have been published to date to document the effect of etching on vital bleaching. In this study, ten patients received a bleaching treatment regimen of several appointments. Half of the teeth in one arch of each patient were etched with phosphoric acid for 20 seconds before they were bleached with 35% hydrogen peroxide. The teeth in the other half of the same arch were treated with tap water prior to bleaching. Evaluations of the patients after 3 and 6 weeks failed to confirm any enhanced lightening effect from etchin