The complexations between human serum albumin (HSA) and the sodium perfluorooctanoate/sodium octanoate and sodium perfluorooctanoate/sodium dodecanoate systems have been studied by a combination of electrical conductivity, ion-selective electrode, electrophoresis, and spectroscopy measurements. The binary mixtures of the surfactants deviated slightly from ideality. Binding plots revealed the existence of two specific binding sites, the first site being more accessible than the second. Positive cooperative binding has been found, thus revealing the importance of the hydrophobic interactions in both kinds of surfactants. The Gibbs energies of binding per mole of surfactant (Delta G((v) over bar)) were calculated from the Wyman binding potential where, on the basis of the elevated number of binding sites, a statistical contribution has been included. Initially these energies are large and negative, gradually decreasing as saturation is approached. Changes in the slope of Gibbs energies have been identified with the saturation of the first binding set. These facts denote that the surfactants under study have different favorite adsorption sites along the protein and that the adsorption process of perfluorooctanoate is more closely followed by dodecanoate than by octanoate. Finally, electrophoresis and spectroscopy measurements suggest induced conformational changes on HSA depending on the surfactant mixture as well as the mixed ratio.