Silver nanoparticles of 23 nm size were formed by chemical reduction of silver nitrate in excess of aqueous sodium borohydride. To examine the aggregation behavior in NaCl solutions, they were coated with poly(diallyldimethylammonium chloride), poly(allylamine hydrochloride) and poly(ethylene glycol) by layer-by-layer assembly. Silver nanoparticles coated with PDADMAC of both high and low molecular weight revealed the lowest stability independent 4 of salt concentration. Silver nanoparticles coated with PAH and PEG are stable in 0.1 or 0.01 m Nacl, whereas addition of 0.5 m NaCl destroys the colloidal solution. The destruction of silver agglomerates and the increase of monodispersity in the case of PEG coated silver nanoparticles were observed after heating at 90 degrees C. In contrast, uncoated silver nanoparticles readily agglomerate and precipitate even after heating at 65 degrees C.