The composition of lead chloride complex ions adsorbed during the underpotential deposition of lead on a polycrystalline gold electrode in 0.1 M NaCl + 10(-4) M HCl was studied by X-ray photoelectron spectroscopy (XPS) and time of flight secondary ion mass spectrometry (TOF-SIMS). Gold electrodes were emersed at 0.3, -0.29, and -0.42 V vs. saturated calomel electrode. Then, either before or after rinsing, the surface concentrations of various species were analyzed using the two vacuum spectroscopic techniques. An adsorbed species with the stoichiometry of PbCl42- was present on the polycrystalline gold electrode just before the underpotential deposition (UPD) region at +0.3 V. The ejection of some adsorbed Cl- and Pb(II) occurred during the UPD Pb discharge process. A mechanism of Pb(II) adsorption and UPD is proposed which is consistent with a parallel electrochemical study.(3) [J. Elecrochem. Sec., 146, 2555 (1999)] Strong adsorption of nitrate ions was detected.