The depletion interaction between two spheres due to nonadsorbing ideal polymers is calculated from the polymer concentration profile using the excess (negative) adsorption. Computer simulations show that the polymer concentration profiles around two spheres are well described by the product function of the concentration profile around a single sphere. From the interaction potential between two spheres the second osmotic virial coefficient, B-2, is calculated for various polymer-colloid size ratios. We find that when the polymers become smaller than the spheres, B-2 remains positive in the dilute regime. This shows that the depletion interaction is ineffective for relatively small spheres.