Bicomponent monolayers composed of amphiphiles having an N-ethylcarbazolyl (ECz) group or an anthryl group were prepared, and energy migration among the ECz groups and energy transfer from the ECz group to the anthryl group in the monolayer was investigated by in situ fluorescence spectroscopy. Fluorescence spectra of the monolayer were measured at various surface pressures. A double-logarithmic plot of the fluorescence intensity of the anthryl group vs the average distance between ECz groups in the monolayer showed a linear relationship with a slope of -6, indicating the occurrence of energy migration via dipole-dipole interaction according to the Forster mechanism. Energy transfer from the monolayer of ECz-containing amphiphiles to cytochrome c in the subphase was also investigated by the same method. Fluorescence from the monolayer composed of zwitterionic amphiphile was quenched by cytochrome c in the subphase. However, the dependence of the quenching rate on the surface pressure was complex and took the maximum value at a molecular area of 160 Angstrom(2)/molecule. Under high surface pressures, cytochrome c should be partially dissociated from the monolayer due to high lateral pressure.