Electrogenerated chemiluminescence (ECL) from the annihilation of rubrene cation and anion radicals has been studied in several organic solvents at temperatures down to -60-degrees-C. The reactants were generated using the triple-potential-step method. Feldberg plot analysis indicates that the emission results from the excited rubrene singlet state produced directly in the electron transfer reaction (S route) and/or from the efficient triplet-triplet annihilation (TTA). In the special case of rubrene the energy of the lowest triplet is almost exactly half that of the first excited single, and the formation of two triplet states (in a single electron transfer act) leads to an efficient TTA (TT route). ECL efficiencies (phi(ecl) in the range 0.01-0.10) have been interpreted in terms of the Marcus theory, taking into account both static and dynamic dielectric properties of the solvent as well as both electronic and vibrational excitations of the reaction products. The rate of the triplet-triplet up-conversion (k(upc) = 1 x 10(10) s-1 within the rubrene triplet-triplet pair) has been also evaluated.