The in vitro bond strengths of three resin cements and a light-cured and a laboratory-processed micro-filled composite were measured. Effects of two surface treatments, and three bond enhancers were analyzed. Resin cements were bonded to sandblasted composite substrates, stored at 37 degrees C in 100% humidity overnight, and debonded in tension. An analysis of variance revealed significant differences among bond strengths. Overall, the composite substrate had the largest effect on bond strength, followed by bond enhancer, cement and, finally, surface treatment. Mean bond strengths ranged from 0.9 to 13.6 MPa. A combination of Concept, Dual Cement, phosphoric acid and Silane produced the lowest mean bond strength (0.9 MPa), while EOS, Dual Cement, hydrofluoric acid, and Heliobond produced the highest recorded mean bond strength (13.6 MPa). In general, the highest bonds were produced using the light-cured composite (EOS), the acrylic monomer (Special Bond II) or the dimethacrylate monomer (Heliobond), the adhesive cement (CR Inlay Cement), and surface treatment with hydrofluoric acid (Comp-Etch). Most of the bond failures (86%) with the laboratory-cured microfilled composite were adhesive. With the light-cured composite, 69% of the failures were mixed adhesive-cohesive types.