Contemporary, third-generation dentinal bonding products have become highly specialized in producing high bond strengths to dentin. This investigation compared in vitro bond strengths of six dentinal bonding systems and their matched composite resins to human enamel and dentin. The effects of treatment by dentinal primers on enamel bond strengths as well as the effects of phosphoric acid on the strengths of dentinal bonds were measured. The use of dentinal primer on enamel improved the bond strengths of Prisma Universal Bond 3/Prisma APH and XR Bond/Herculite systems and had no effect on Denthesive/Charisma, Scotchbond 2/Silux, and Tenure/Perfection, while the enamel bo nd strengths of Gluma/Pekalux declined. Pretreatment of dentin with phosphoric acid improved the bond strengths of Denthesive/Charisma, Prisma Universal Bond 3/Prisma APH and XR Bond/Herculite, but had no effect on Gluma/Pekalux, Scotchbond 2/Silux and Tenure/Perfection.