Objective: Historically, wide variations in the shear bond strength of resin composite bonded to dentin have been reported. The purpose of this study was to compare 5 commercially available single-bottle dentin bonding systems while controlling several sources of variation in shear bond strengths. Method and materials: Extracted molars were stored for 2 weeks in 0.5% Chloramine T. The teeth were mounted, the occlusal enamel was removed to expose middle dentin, and the exposed dentin was etched and treated according to 1 of 6 protocols. Finally, a cylinder of resin-based composite was bonded to the dentin. After 24 hours, specimens were fractured under shear force, and the results were recorded in megapascals. Results: The type of product used was significantly associated with the mean shear bond strength observed. All products exhibited some degree of variation from specimen to specimen. One product, PQ1, exhibited less variation than the other 4 products. Conclusion: PQ1 was found to have a significantly higher mean shear bond strength than the other 4 products tested. There was no significant difference between specimens bonded to dry dentin and specimens bonded to wet dentin when using PQ1.