The dilational rheological behavior of gelatin molecules adsorbed at the air-water inter-face has been studied as a function of sodium dodecyl sulfate (SDS) concentration for a 7 wt % gelatin-SDS solution at 40 degreesC. Binding of SDS molecules to the gelatin strands disrupts the cross-linked network structure of adsorbed gelatin molecules and results in a reduction of the surface elastic modulus of the adsorbed layer that continues until the bulk SDS concentration reaches 1 mM. Beyond this SDS concentration, the dilational rheological properties of the adsorbed gelatin layer are indistinguishable from those of pure SDS adsorbed layers.