A theory is derived for the non-Newtonian behavior of a dilute suspension of neutrally buoyant, rigid, spherical inclusions in an incompressible Newtonian fluid. The source of the non-Newtonian effects is shown to be that portion of the kinetic energy associated with the flow perturbation caused by the presence of the particles. Explicit forms are given for the average stress constitutive relation under the restriction of slowly varying flow conditions. Related normal stress effects are considered in some detail for the case of simple shearing flow.