The adsorption of cationic polyelectrolytes onto negatively charged mica from solutions of variable ionic strength was studied using the interferometric surface force technique. The results show that the structure of the adsorbed layer of polyelectrolyte is strongly dependent on the ionic strength of the solution from which the initial adsorption takes place, rather than the valency of the counterion. Within the time for one experiment (1 week) it was not feasible to achieve the same layer structure by a stepwise increase of the ionic strength, as was obtained when the adsorption of the polyelectrolyte was carried out directly from the solution of the higher ionic strength. A mechanism for attraction due to counterion bridges when large, flexible counterions are present in the solution is suggested.