Tensile bond strength tests are commonly used for the evaluation of adhesive dental materials. The majority of these tests are carried out after 24 h of storage in water. However, determination of the early tensile bond strength could be more important, especially in relation to gap formation between the cavity surface and the restorative material. This study investigated the tensile bond strengths of five enamel/dentin bonding systems and two experimental dentin bonding systems. Tensile bond strengths were obtained at one min, ten min, and 24 h after the resin composite was cured. Bond strengths at the early stages were always somewhat less than the 24-hour test results. For the enamel/dentin bonding systems, a significant difference was found between the enamel and dentin bond strengths at all time periods, except with Superbond D-liner and Liner Bond. The experimental group with glyceryl methacrylate as the primer produced a good 24-hour result (14.3 MPa), but the early bond strengths were no different from those in the non-primer-treated groups. It was concluded that this material may actually retard the polymerization of the bonding resin. Previous workers have suggested that a tensile bond strength in the order of 20 MPa is necessary for gap-free restorations to be obtained. Should this be the case, then all of the materials tested, from the aspect of early bond strength, lack the strength for prevention of gap formation, although Superbond D-liner and Liner Bond approached this hypothetical figure. These systems, Superbond D-liner and Liner Bond, also exhibit small differences between the enamel and dentin tensile bond strengths.