Purpose: The shear bond strength of an auto-polymerizing poly(methyl methacrylate) denture base resin material to cast titanium and cobalt-chromium alloy treated with six conditioning methods was investigated. Materials and Methods: Disk specimens (10 mm in diameter and 2.5 mm in thickness) were cast from pure titanium and cobalt-chromium alloy. The specimens were wet ground to a final surface finish of 600 grit, air dried, and treated with the following bonding systems: 1) air abraded with 50-70-µm-grain alumina (SAN); 2) air abraded with 50-70-µm-grain alumina + conditioned with Alloy Primer (ALP); 3) air abraded with 50-70-µm-grain alumina + conditioned with AZ Primer (AZP); 4) air abraded with 50-70-µm-grain alumina + conditioned with Estenia Opaque Primer (EOP); 5) air abraded with 50-70-µm-grain alumina + conditioned with Metal Link Primer (MLP), and 6) treated with ROCATEC system (ROC). A denture base material (Palapress Vario) was then applied to each metal specimen. Shear bond strengths were determined before and after 10,000 thermocycles. Results: The strengths decreased after thermocycling in all combinations. Among the treatment methods assessed, groups 2 and 4 showed significantly (p 0.05) enhanced shear bond strengths for both metals. In group 4, the strength in MPa (n = 7) after thermocycling for cobalt-chromium alloy was 38.3, which was statistically (p 0.05) higher than that for cast titanium (34.7). Conclusion: Air abrasion followed by the application of two primers containing a hydrophobic phosphate monomer (MDP) effectively improved the strength of the bond of denture base material to cast titanium and cobalt-chromium alloy. Keywords: cobalt-chromium, denture base material, primer, poly(methyl methacrylate), shear bond strength, titanium