Electrochemical impedance spectroscopy technique was applied to study bilayer membranes formed with egg yolk phosphatidylcholine containing as an additional component one of two carotenoid pigments: canthaxanthin or beta-carotene. The results show that both carotenoids present in the lipid membranes at relatively low concentration modify significantly electrical capacitance and electrical resistance of the membranes. Domain structures appear as a result of interactions between components within analyzed bilayers. The equilibrium of domain formation can explain the deviation from the additivity rule. This equilibrium was described by mathematical equations as well as verified experimentally. Moreover, the surface area of domains was calculated and their stoichiometry was proposed.