Coadsorbing poly-L-lysine hydrobromide inhibits hexadecyltrimethylammonium bromide adsorption to silica surfaces. Using optical reflectometry to measure surface excess concentrations, we fmd that this inhibition depends on the concentration of added I:I electrolyte, both quantitatively and qualitatively. In the absence of added salt, the polyelectrolyte causes a rather uniform decrease in the extent of surfactant adsorption, and the shape of the surfactant coadsorption isotherm is qualitatively similar to the isotherm for adsorption in the absence of polyelectrolyte. In particular, the surfactant concentration marking the onset of cooperative adsorption, where admicelles are formed at bulk concentrations below the critical micelle concentration, is unchanged by the presence of the polyelectrolyte. In contrast, when the surfactant coadsorbs in the presence of 10 mill KBr, the polyelectrolyte eliminates this adsorption regime altogether. Admicelles do not form until the bulk surfactant concentration exceeds the critical micelle concentration. Upon addition of the 1:1 electrolyte, the inhibition mechanism changes from a simple competition for available surface area to a more profound disruption of surfactant interfacial self-assembly. By comparing a low molecular; weight oligolysine with three higher molecular weight polylysine samples, we find that this change in inhibition mechanism can be traced to the effect of salt on the relative adsorption energies of the surfactant and the polyelectrolyte, but kinetically trapped or frustrated states exert a large influence on the composition of the mixed adsorbed layer in the case of higher molecular weight polyelectrolytes.