The interaction of DNA damaged by the antitumor drug cis-dichlorodiammine platinum(II) (cisplatin, cis-DDP) with the nonhistone chromosomal proteins HMGB1 and HMGB2 was studied using circular dichroism spectroscopy. It was shown that the CD spectra of the complexes indicates weak increase of a-helical content of the protein molecule typical for the binding of the HMGB-domain to native DNA. The presence of cisplatin prevents the formation of the ordered supramolecular structures of DNA in the complexes.