In the bimodal model of the viscoelastic behavior of a bimodal suspension with a colloidal size fine fraction and a noncolloidal size coarse fraction, the two fractions behave independently of each other when the particle size ratio is large : The colloidal fraction is solely responsible for the non-Newtonian behavior while only hydrodynamic interaction takes place between the coarse particles. Measurements performed on a bimodal suspension and on a suspension of noncolloidal particles in a polymeric liquid indicate that the non-Newtonian behavior originates from the colloidal fraction in the former and from the polymeric liquid in the latter. The results support the validity of the concepts behind the bimodal model.