Purpose: Despite many published articles on the bond strength of self-etching primers and adhesives in the restorative dentistry literature, there have been relatively few laboratory studies of the bond strength of new orthodontic materials, and, in most of these published studies, investigators used various methodologic approaches during different stages of the in vitro testing procedures. The aim of this study was to compare the shear bond strength of 4 self-etching primer and adhesive formulations, a nonrinse conditioner and acetone adhesive system, and a conventional system. Material: The self-etching products tested were Prompt L-Pop (3M ESPE, Seefeld, Germany), Clearfil SE Bond (Kuraray Dental, Osaka, Japan), FL Bond (Shofu Dental, Kyoto, Japan), and One-Up Bond F (Tokuyama, Tokyo, Japan); the nonrinse conditioner and acetone-based adhesive system was NRC and Prime&Bond NT (Dentsply International, Konstanz, Germany); the conventional acid-etch and bond system was Transbond XT (3M Unitek, Monrovia, Calif). Brackets were bonded to intact bovine mandibular incisors (n = 7 per group) according to each manufacturer's recommendations. The specimens were first stored in deionized water at 37 degrees C for 24 hours and then subjected to thermal cycling in deionized water at 5 degrees C +/- 2 degrees C to 55 degrees C +/- 2 degrees C for 1000 cycles. To facilitate degradation of bonds, the specimens were further stored in distilled water for 6 weeks before debonding procedures. Results: The shear bond strengths of the 5 experimental groups were all significantly lower (P < .05) than that of the control group (Prompt L-Pop, 1.72 +/- 0.13 MPa; Clearfil SE Bond, 1.75 +/- 0.19 MPa; FL Bond, 1.71 +/- 0.22 MPa; One-Up Bond F, 1.77 +/- 0.14 MPa; control, 10.5 +/- 0.86 MPa) but not different from one another (P > .05). Conclusions: The tested self-etching primer and adhesive systems produced bond strength values much lower than that of the control product. Clinically, these products might not be suitable for orthodontic bracket bonding in terms of the shear bond strength achieved after thermal cycling and water storage.