AbstractThe coupling constant λ from the recently derived semiempirical equation for the superconducting transition temperature Tc3 = 0.5γDQD exp (−2/λ) is identified with the effective electron—electron—phonon coupling constant λexp measured in the experiment. Under this assumption the McMillan equation for Tc is written in terms of λ*, the electron—phonon coupling constant and μ*, the electron—electron interaction parameter. The method of determination of λ* and μ* from the measured λexp is presented and a numerical verification is given.