Flash photolysis study was carried out of electron transfer during rho-benzoquinone-photooxidation of monomeric and aggregated molecules of chlorophyll "a" in aqueous solutions of serum albumin and triton X-100. It has been found that in the presence of rho-benzoquinone oxidation of monomeres and aggregates of chlorophyll takes place; it results in the formation of the pigment cation-radicals. The kinetic analysis of the pattern of electron transfer during aggregates photooxidation enables a conclusion that oxidation proceeds only via the triplet state of the pigment molecules. Study of the transformation of cation-radicals of monomeres and aggregates showed a difference in the death of radicals. For chlorophyll monomeres the death of cation-radicals is described by the 2nd order equation and is conditioned by the recombination of ion-radicals of the pigment and acceptor. The death of aggregate cation-radicals proceeds according to the 1st order reaction. The results obtained point to possible participation of chlorophyll triplet state in primary photochemical reactions of photosynthesis.