A new b-type cytochrome, termed cytochrome b560 according to the wavelength maximum of its alpha-band in the reduced minus oxidized difference spectrum, was isolated from eggs of whitefish and partially purified by fractionation of the water-soluble moiety of yolk. The absolute absorption spectrum of reduced cytochrome b560 has maxima at 426, 529 and 560 nm and that of the oxidized form at 416 nm. The reduced minus oxidized difference spectrum has maxima at 428, 529 and 560 nm. The midpoint potential of this cytochrome is +193 mV. Based on the MCD spectra of reduced cytochrome and the optical absorption spectra in the visible region of the oxidized cytochrome, it is suggested that the heme iron in cytochrome b560 has two histidine imidazoles as the 5th and 6th axial ligands.