Calorimetric titrations in benzene and chloroform at 298.15 K have been performed to give the complexes stability constants and the thermodynamic parameters for the complex formation of nature iron(III)porphyrins with pyridine. Stoichimetry of the complexes formed has been determined. It has been found that the thermodynamic parameters obtained depend on nature of peripheral substituents of the porphyrins. The estimation of the influence of Cl- and Ac- ions on the processes studied has been carried out. Using thermodynamic analysis method, the crystallsolvates of nature iron(III)porphyrins with benzene have been studied. Stoichiometry, thermal and energetic stability of the pi-pi-complexes formed have been determined. The data obtained have been used to the estimate solvent effect on the thermodynamic parameters of axial coordination of pyridine on the iron(III)porphyrins in benzene. (C) 2003 Elsevier Science B.V. All rights reserved.