Bulky, open assemblies, prepared from the sequential adsorption of oppositely charged polyelectrolytes (PE), could potentially be used as receptor matrixes in biosensing devices. We have examined the building of such structures onto gold surfaces from water-soluble cationic and anionic polyelectrolytes of different chemical structures, molecular weights (5 x 10(4) to 1.5 x 10(7)), and charge densities (20-100%) using quartz crystal microgravimetry and atomic force microscopy. The effects of molecular weight were found to be small compared with the effects of charge density. When the charge density on the cationic PE was decreased, the number of PE layers that could be reliably deposited also decreased, bt the same time the film became much more open and heterogeneous. The integrity of film fabrication improved with increasing solution ionic strength, confirming the key role of counterions.