A stable aqueous lead sol (10 nm particles) is formed upon the gamma-irradiation of Pb(ClO4)(2) in the presence of (poly)ethyleneimine. Lead nanoparticles have an absorption band at 218 nm with epsilon = 3.2 x 10(4) M-1 cm(-1); the band appears at the wavelength that is expected for a surface plasmon oscillation. The changes in the shape of the absorption band, which occur upon the interaction of the nanoparticles with various solutes, are described and interpreted. Oxygen, nitrous oxide, carbon tetrachloride, and chloroform oxidize colloidal lead particles to Pb2+. Carbon disulfide oxidizes only surface lead atoms to yield a layer of PbS precursor. The oxidation of lead particles by the ions of noble metals is investigated for Ag+ and Cu2+. Silver ions oxidize lead nanoparticles incompletely, which is explained by the formation of mixed Ag-Pb structures. Cu2+ ions also do not completely oxidize lead particles, although Cu particles with a low Pb content can be obtained.