In clinical practice it is difficult to keep acid etchants off the dentinal surface during bonding procedures. If the acid etchant could be used as part of the overall conditioning system, technique sensitivity would be reduced. This paper reports the data obtained with the use of phosphoric acid as a dentin-enamel conditioner in a bonding system developed by the author. In vitro bond strength and microleakage were examined using Dual Cure Scotchbond as a control. In both ests, the experimental group showed statistically significantly better results than did the control. A clinical study of 140 Class II restorations showed no postoperative sensitivity, and all teeth were vital after 18 months.