In this work, the influence of the chemical structure of a group of cationic polymethine photosensitizers synthesized in the spectroscopy laboratory of the Institute of Applied Physical Problems, them. Sevchenko BSU, on their distribution among serum proteins. Using the method of gel chromatography, it was established that the initial indotricarbocyanine dye PD154 binds mainly to serum albumin molecules. The chemical modification consisting in replacing the two carboxyl groups with polyethylene glycol molecules (300 kDa) leads to an increase in the affinity of PD220 for lipoproteins, and the use of an unsubstituted polymethine chain blocks the binding of PD222 to serum proteins. Spectral measurements have shown that in aqueous solutions of PD154 and PD220 dyes, a strong (20-25 nm) bathochromic peak of the absorption spectra is observed when blood serum is added. At the same time, the dye PD222 does not react to the presence of serum in the solution. Analysis of individual protein fractions stained with dyes showed a significant effect of the type of whey protein in the complex with polymethine dyes on the spectral characteristics of the latter. The appearance of a short-wave peak in the absorption spectra of the dye-albumin complexes was established. Possible biophysical mechanisms of the processes leading to the observed behavioral features of polymethine dyes in the presence of serum proteins, as well as the possibility of their use in biomedical purposes, are discussed.