Resonance Raman spectra of the haem group of 8 × 10−5 M horse heart ferro- and ferricytochrome c solutions have been obtained. The spectra are almost identical to that of haemoglobin. The frequency of the Raman line near 1370 cm−1, which in haemoglobin is sensitive to the position of the haem iron, indicates that the iron atom of cytochrome c lies in the plane of the porphyrin for both oxidation states.