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X-Ray photoelectron spectroscopy (XPS) data of Pd clusters in Nay, MgY and HY zeolites show that t h e chemical shift of t h e Pd 3d,,, line is dependent on t h e concentration of the protons and their position in the zeolite. The positive charge or 'electron deficiency' of t h e Pd particles is significant even for Pd/NaY which contains only t h e protons created by H, reduction of Pd2+ ions. In these samples t h e Pd 3d,,, binding energy exceeds that of neutral Pd by ca. 0.4 eV. The positive charge of the Pd clusters is much higher in HY and MgY, reflecting t h e higher proton concentration in the supercages; t h e binding energy is shifted by 0.8 eV. Additional relevant information on t h e metal cluster environment is obtained from analysis of the Auger parameter of Pd. It decreases with increasing number of protons interacting with t h e Pd particles, and it increases upon substituting protons by polarizable ions, e.g. Na+ or NH;. These data are consistent with t h e model which suggests that metal-proton adducts, [Pd,-H,]"+ with rn 3 1, are formed in proton-containing zeolites.