Validity on the well-known Onsager reciprocal relations L[sub 12] = L[sub 21] is verified in the kinetic theory of gases taking into account mass and heat transfer near the surface. Using an analytical solution to the ellipsoidal statistical equation (providing for the true Prandtl number), it is demonstrated that the Onsager relations are obeyed, at least to within exponential corrections of the type exp(-1/Kn) in the Knudsen number.