Bimetallic monolayer-protected nanoparticles have been synthesized by the core metal galvanic exchange reaction of dodecylthiolate monolayer-protected metal (Ag, Pd, Cu) clusters with the more noble metal metal thiolate complexes Au-I[SCH2(C6H4)C(CH3)(3)] and Pd-II[S(CH2)(11)CH3)(2)]. The bimetal nanoparticles produced are stable and can be isolated without core aggregation or decomposition. These new materials have been examined by UV-vis spectroscopy, transmission electron microscopy, X-ray photoelectron spectroscopy, and elemental analysis. Their optical properties reflect bimetal cluster formation by time-dependent shifts in the surface plasmon resonance absorbance. Transmission electron microscopy results suggest that the core metal replacement can also effect a change in nanoparticle core size. Formation of bimetallic nanoparticles appears to stabilized the less stable member of the metal pair.