Mechanisms of interaction between antitumor compounds and biological molecules have been being studied for decades. One of the most widely applicable drug is dichlorodiammineplatinum(II) (DDP). In the present work we have analyzed effect of cis- and trans-DDP on secondary structure of DNA, bovine serum albumins and HMGB proteins using FTIR spectroscopy. We have shown that both of the DDP isomers facilitate the formation of albumin dimers. We have also shown that DDP facilitates changes in DNA structure, attributed to DDP binding to DNA bases and DNA cross-linking. Thus, the application of hidden peak analysis of FTIR spectra shown to be informative to structural investigation of DDP complexes with nucleic acids and proteins.