The interaction of meso-tetra(4-N-hydroxyethylpyridyl)porphyrin, meso-tetra(3-N-hydroxyethylpyridyl)porphyrin, and their zinc complexes with bovine serum albumin (BSA) was studied by electronic spectroscopy, CD, and equilibrium dialysis at pH 7.2. The titration of the porphyrins with BSA was accompanied by a decrease in light absorption and a bathochromic shift of the Soret band, as well as by the appearance of an isobestic point. The porphyrin interaction with BSA also led to the induction of positive CD spectra in the visible region, which is explained by the porphyrin sorption on the protein globule. The equilibrium dialysis helped in determining the stoichiometry of binding and the binding constants of the porphyrins under study with BSA using Scatchard plots. This interaction is nonspecific and reversible. The English version of the paper: Russian Journal of Bioorganic Chemistry, 2004, vol. 30, no. 2; see also http://www.maik.ru.