STATEMENT OF PROBLEM. The poor chemical bonding of a denture base resin to cast titanium framework often introduces adhesive failure and increases microleakage. PURPOSE. This study evaluated the shear bond strengths of a heat cure denture base resin to commercially pure titanium, Ti-6Al-4V alloy and a cobalt-chromium alloy using two adhesive primers. MATERIAL AND MATHODS. Disks of commercially pure titanium, Ti-6Al-4V alloy and a cobalt-chromium alloy were cast. Specimens without the primer were also prepared and used as the controls. The shear bond strengths were measured on a screw-driven universal testing machine. RESULTS. The primers significantly (P < .05) improved the shear bond strengths of the heat cure resin to all metals. However, the specimens primed with the Alloy primer? (MDP monomer) showed higher bond strength than those primed with the MR bond? (MAC-10 monomer) on titanium. Only adhesive failure was observed at the metal-resin interface in the non-primed specimens, whil