Starting with an analytic representation of the electron d. from a Hylleraas wavefunction we have obtained an analytic representation of the exchange-correlation potential of the helium atom. This, essentially exact, exchange-correlation potential has been employed to test a recently developed approach, named DFT-SAPT, which combines symmetry-adapted perturbation theory of intermol. interaction energies with a d. functional theory description of the interacting monomers. In DFT-SAPT all of the second-order contributions including the exchange corrections are detd. from coupled-perturbed d. functional theory. Comparison of the results for the helium dimer to previous high-quality supermol. and intermol. perturbation theory results demonstrates the success of the new approach.