- The solute enhancement factor B was calculated for b.c.c. alloys containing small concentrations of solute (<2at%). Only the second term in the equation D2(c) = D2(0) [1 + B1c + B2c2 + …] was taken into consideration. D2(c) and D2(0) are the solution diffusion coefficients in the alloy and in the pure solvent, respectively. It is shown that if the absolute value of B1 > 5 the other terms in the above equation cannot be neglected if the convergence of the series is to be maintained. Experimental values for B are considered and are compared with theoretical estimations. The derived equation for B is given by B = (3 ω12/ω2 exp (— Δgp2/kT) + 4 ω24/ω2) exp (—Δg1/kT) + (3 ω21/ω2 exp (— Δgp1/kT) + 3 ω′24/ω2) × exp (— Δg2/kT) + 4 ω23/ω2 exp (— Δgp1/kT) + 3 ω′23/ω2 exp (— Δgp2/kT) — 20, where ω are the jump frequencies, Δg are the additional free energies to form a vacancy at a specific neighboring site and the Δgp are the negative of the binding energies between two solute atoms.