A molecule of Penicillium vitale catalase is shown to dissociate into subunits with the molecular weight 75-80 kDalton. When hemin is splitted off the molecule also disintegrates into subunits equalling 1/4 of the enzyme molecule. The amino acid composition and fingerprints of the catalase subunits were studied. It is supposed that N-terminal residue of the subunit is blocked.