An equation has been derived to compare the costs of two schemes for recycling spent fuel to light-water reactors: diffusion and blending. The calculations show that blending is slightly more costly than diffusion. The factors that can chiefly influence this conclusion are the discharge enrichment and the value of 236U. A very high burnup would favor diffusion; a very high price for 238Pu and, therefore, for 236U, would render blending the desirable route.