The adsorption of O2, N2, CO, and N2O on polycrystallinezirconium has been studied using ESCA and AES over a wide temperature range from room temperature to nearly the melting point of zirconium. The gases adsorb dissociatively at all temperatures studied, and the room temperature sticking coefficients are low (<0.01). Heating causes migration of the adsorbate species into the bulk zirconium. Two distinct surface phases (states) of zirconium are identified. State 1 exists when the sample has not been heated above the h c p↔b c c transition temperature of 1135 K for prolonged periods while state 2 occurs after prolonged heating (the time is a function of temperature) above the transition temperature. The AES spectra and chemisorptionproperties of the two states are very different. State 1 AES spectra show a prominent 175 eV peak which is nearly gone in state 2 AES spectra. State 1 readily adsorbs CO and N2 at room temperature while state 2 adsorbs relatively small amounts of CO and is almost inert to N2. Therefore, the valence electrons responsible for the AES 175 eV peak play a significant role in the chemisorptionproperties of zirconium.