Silver clusters and nanoparticles were prepared by reduction of silver nitrate by sodium borohydride in water, in the presence of polyacrylate ions, and in inverse micellar solutions consisting of Laureth 4 and water. Thr: kinetics of formation of Ag-4(2+) aggregates and Ag-9(+) in the presence of polyacrylate ions could be observed by the stopped-flow technique, and die characteristic UV absorption spectra of the respective stable clusters were recorded, The formation of these species was critically dependent on the manner in which reactants were combined. The silver nanoparticles prepared in the inverse micellar solutions using different mixing procedures were characterized via UV-vis spectra, dynamic light scattering, and transmission electron microscopy. The results showed that the procedure of adding aqueous sodium borohydride solution into the inverse micellar solution containing silver nitrate gave the most uniform spherical silver nanoparticles. The reaction kinetics of this procedure was investigated through UV-vis spectra, which indicated that the generation of silver nanoparticles occurred in parallel with the disappearance of smaller clusters, and was characterized by a single exponential with a time constant of about 18 s, followed by aggregation into much larger particles.