To evaluate enamel bond strengths of self-etching primer systems with and without the use of phosphoric acid etching. The enamel of sixteen bovine incisors was ground with wet 600-grit SiC paper, and specimens were divided into seven groups. Group SE and group ABF were bonded with Clearfil SE Bond (Kuraray) and an experimental self-etching primer system ABF (Kuraray) in accordance with the manufacturer's instructions. The enamel of groups SE+AC and ABF+AC was acid-etched (AC) prior to application of the primers. The enamel of groups AC+SE-P and AC+ABF-P was acid-etched and the bonding resin was applied without primer. All of these groups were restored with Clearfil AP-X (Kuraray). For the control group (SB), enamel was etched and bonded with Single Bond (3M) according to manufacturer's instructions and restored with Z-250 (3M). After 24 h of water storage, the teeth were sectioned into 0.7-mm-thick slabs, trimmed for microtensile bond testing and subjected to tensile forces at a crosshead speed of 1 mm/min. After testing, all samples were analyzed with SEM. Data were evaluated by one-way ANOVA and Fisher's PLSD (α = 0.05). Acid etching prior to application of the self-etching primer produced higher bond strengths to enamel than self-etching priming only. Omission of the primer step provided bond strengths similar to the other acid-etched groups. SEM analysis revealed that when the acid was applied prior to the self-etching primers, an increase in failure within enamel occurred. Since high bond strength to enamel is critical for good margins and seal of the restorations, applying the etching step should be considered in case of restorations that rely mainly on enamel bonding.