Using isotopic substitution, the small-angle neutron scattering from a gelatin layer preadsorbed upon polystyrene latex has been measured as a function of the added concentration of sodium dodecyl sulfate (SDS). The data have been fitted using a model which includes an exponential volume fraction profile and a term to account for the scattering from spatial concentration fluctuations. Measurements indicate that the gelatin layer thickness increases to a maximum as a function of SDS concentration, while the volume fraction of gelatin adsorbed at the interface simultaneously decreases. Consequently, the adsorbed amount of gelatin peaks at SDS concentrations equivalent to approximately one SDS micelle/gelatin chain. Further addition of SDS sees the adsorbed amount decay below that of the system in the absence of SDS. At the highest SDS concentrations, the gelatin also develops a scattering form similar to that of SDS micelles.