The intermolecular interaction of bacteriochlorophyll c and its pheophytin was studied in nonpolar solvents and solid films with the aid of absorption and IR (in the region of 1800-1600 and 3800-3000 cm-1) spectra. The influence of water removal and its addition on these spectra was investigated. The effects of pyridine treatment and pigment concentration were also examined. The self-assemblage of all types of bacteriochlorophyll c aggregated forms absorbing in the range 680-745 nm is due to the formation of intermolecular bonds in which keto groups of cyclopentanone rings and perhaps hydroxyl (hydroxyethyl) groups of the 1st pyrrol rings take part. Keto groups form coordinate bonds with the central Mg atom (keto-C.dbd.O.cntdot..cntdot..cntdot.Mg). Hydroxyl groups interact coordinately with Mg and simultaneously form H bonds with pyrrol N. In contrast to chlorophyll a and bacteriochlorophyll a, water molecules in the case of bacteriochlorophyll c do not particpate in intermolecular bond formation in the production of long-wave aggregated forms. The thermostability of bacteriochlorophyll c aggregates and their rather high stability to disaggregating agents is related to the peculiarities of their structure. Bacteriopheophytin c in any state (solution or solid film) is not capable of forming intermolecular bonds by its carbonyl groups and long-wave aggregates. The specific features of the assemblage of bacteriochlorophyll c aggregates modeling antenna of the green photosynthetic bacteria are discussed.