The validity range of the momentum approximation in binary collisions : s investigated. It is shown that at high energies,E≳ 10 ·Z1Z2e2/aTF, the approximation is even applicable to scattering angles ϑ as large as 60 degrees. An empirical formula for the evaluation of the momentum approximation employing the Thomas-Fermi-Moliére potential is given. It reduces the computer time to calculate ϑ to ∼⊥10of the time consumed in using the standard algebraic functions appearing in the momentum approximation.