The adsorption process of cytochrome c from aqueous solution onto glass and its desorption process from glass into water were investigated by broad-band, time-resolved optical waveguide spectroscopy. The adsorption and desorption rate constants as well as the adsorption free energy of cytochrome c were determined by fitting the Soret-band absorbances measured at different adsorption and desorption times to the Langmuir isotherm. The surface coverage of immobilized protein molecules at equilibrium was calculated on the basis of the waveguide theory.