Here we report a novel pathway for the synthesis of silver nanoparticles. Spontaneous reduction of silver 2-ethylhexanoate [Ag(ethex)] takes place in dimethyl sulfoxide (DMSO) at room temperature. The reaction is slow and markedly depends on temperature leading to the formation of silver nanoparticles (NPs) with a surface plasmon resonant band maximum centered at 424 nm. Colloidal silver is not stable in DMSO without stabilizing agents. When sodium citrate (1 x 10(-4) M) is utilized as a capping agent, the surface plasmon shifts to 414 nm and the surface-modified silver nanoparticles are stable for more than 6 months. The resulting nanoparticles are quite stable but at the same time reactive enough for catalytic purposes. An HR-TEM study shows a nanoparticles size distribution centered in 4.4 nm of diameter (SD = 1.2) and a considerable number of defects such as stacking faults and twined particles. From ab initio quantum mechanical calculations, we propose a possible precursor for the spontaneous reduction of [Ag(ethex)] in DMSO. In addition, the interaction between NO and silver nanoparticles was tested. UV-visible spectra show the oxidation of silver and the reduction of NO at room temperature. The most probable products of this reaction are N2O, molecular nitrogen, and oxygen. Therefore, we have a simple catalytic colloidal system for NO.