CD and MCD spectra of bovine liver catalase and its derivatives were studied over the wavelength range from 250 to 500 nm. Native catalase showed a large negative CD peak in the Soret region which was comparable with that of other hemoproteins, except for methemoglobin and metmyoglobin. The Soret CD peak of the peroxide derivatives of catalase was similar to that of native catalase, while the Soret MCD peak of native catalase was smaller in magnitude than that of other hemoproteins. The MCD peak of the cyanide complex of catalase showed a magnitude about half that of methemoglobin and metmyoglobin. The difference in the magnitude of the MCD peak among hemoproteins is thought to be caused by an endogeneous ligand other than iron-histidine interaction at the fifth coordination position. The magnitude of the MCD peak of low-spin ferric derivatives in the Soret region was considerably larger than that of high-spin ferric derivatives. Conversion of native catalase to the peroxide compound I caused only a small change in the MCD spectrum in the Soret region, while reduction of compound I to compound II was accompanied by a major change in the Soret MCD spectrum. In the near ultraviolet region, CD and MCD spectra of native catalase and its derivatives did not exhibit any evidence of a heme-related peak, the magnitude of which was not altered by ligand substitution. It is suggested that a heme iron-amino acid residue(s) interaction other than heme-histidine interaction is present.