Purpose: The aim of this study was to evaluate the influence of ultrasonic treatment on the microtensile bond strength of self-etching adhesives to dentin. Materials and Methods: Forty-two human molars were wet ground occlusally until dentin was exposed. Clearfil S3 Bond, Futurabond NR (one-bottle) and Clearfil SE Bond (two-bottle) self-etching bonding systems were used in this study. In control groups, bonding procedures were performed according to the manufacturers' instructions. In the experimental groups, bonding materials were applied with an ultrasonic scaler. When using Clearfil SE Bond, the ultrasonic device was used either during priming or the bonding stage. The composite was then built up to 5 mm in height. Each tooth was serially sectioned into rectangular beams. The beams were categorized also according to positional status as marginal or central. Beams were subjected to microtensile testing after 24 h of water storage. Failure modes were observed with a stereomicroscope and classified. Randomly selected tested beams from each group were examined with SEM. Results: Three-factor ANOVA results indicated that the adhesive bonding system had a significant effect on bond strength (p 0.001), whereas ultrasonic agitation and the position of the tested beam (marginal vs central) had no effect on bond strength (p > 0.05). Failure after the test was commonly due to adhesive breakdown associated with partial cohesive failure in the dentin. The mean (SD) microtensile bond strengths to dentin for S3 Bond, Futurabond NR, Clearfil SE Bond in the control group were 44.3 (11.7), 35.3 (12.0), 25.1 (8.8), resp, and in the ultrasonic group 39.3 (14.2), 31.3 (13.5), 35.5 (13.5) at priming and 32.6 (16.2) at bonding. Conclusion: Ultrasonic agitation during application of self-etching adhesives had no effect on bonding performance of the self-etching adhesive. Schlagwörter: composite resin, dentin, ultrasonic, dentin bonding agents, self-etching, single-step adhesives