Purpose: To evaluate the influence of contamination and plasma treatment on the bond strength of resin to zirconia ceramic. Materials and Methods: After immersion in saliva or the use of a silicone disclosing agent, polished and airborne-particle abraded zirconia specimens were cleaned either ultrasonically in 99% isopropanol or with nonthermal plasma. Uncontaminated zirconia specimens were used as control. For chemical analysis, specimens of all groups were examined with x-ray photoelectron spectroscopy (XPS). Plexiglas tubes filled with composite resin were bonded to ceramic specimens with a phosphate-monomer-containing luting resin. The influence of contamination and cleaning methods on ceramic bond durability was examined by tensile testing after 3 and 150 days of water storage, with an additional 37,500 thermocycles during the 150-day storage. Results: XPS showed an increase in the amount of oxygen and a decrease in the amount of carbon on the zirconia surface after plasma treatment. After contamination with silicone, XPS revealed a high amount of Si residue on the surface that none of the investigated cleaning processes could completely remove. The tensile bond strength to uncontaminated zirconia ceramic was durable, but was significantly reduced by contamination. Conclusion: Plasma treatment was effective in removing salivary contamination but not silicone disclosing agent residue from the bonding surface of zirconia. Keywords: zirconia, contamination, bonding, plasma treatment