We studied the interaction of cytochrome c (cyt c) with unilamellar liposomes (ULL) composed of dimyristoylphosphatidylcholine (DMPC) modified by calix[6]arene (CX). We also analyzed the influence of cyt c on the properties of monomolecular films on an air-water interface composed of CX. The changes of the liposome size have been studied by dynamic light scattering and the zeta potential was determined by Doppler velocimetry. By ultrasound attenuation coefficient we also studied the effect of CX on the phase transition of the lipid bilayer of liposomes. The liposomes containing 10mol% CX have been on average 1.5 times larger in comparison with unmodified ULL. The increase of ULL diameter has been accompanied by a decrease of zeta potential toward negative values. This has been due to negatively charged carboxyl groups of CX polar part. The interaction of cyt c with CX resulted in an increase of zeta potential. CX did not affect the phase transition temperature of liposomes (T = 24.4 °C). However, the half width of the transition peak increased which is evidence of a decrease of the cooperativity of phase transition. CX forms stable monomolecular films on the air-water interphase. The presence of cyt c in a water subphase caused an increase of mean molecular area of CX. The dependence of relative changes of the area per molecule as a function of cyt c concentration had the shape of Langmuir isotherm. The dissociation constant, KD, determined in a solid state of the monolayer was 26.0 ± 5.4 nM, which is evidence of good affinity of cyt c to CX., Tibor Hianik, Zuzana Garaiová, Veronika Vargová, Pavol Vitovič., and Obsahuje bibliografii