Experimental tests of a few constitutive models were performed on the basis of time‐dependent stress data for an 8% polystyrene solution in chlorinated biphenyl. The strain‐dependent relaxation modulusGwas measured with a cone‐and‐plate relaxometer. The shear stress σ and the first normal stress differenceν1at the start and on the cessation of shear flow were evaluated from previous results of flow birefringence measurement. The BKZ model consistently described the relation between σ andν1on the cessation of shear flow. A BKZ relation, corresponding to the van Es‐Christensen relation for the rate‐dependent constitutive model, held good for the stresses at the start of shear flow. The BKZ model calculation starting fromGgave σ andν1slightly different from those observed at high rates of shear. The deviation may be removed by allowing a slight rate dependence of the memory function as was done by Macdonald. The model of Acierno‐La Mantia‐Marrucci‐Titomanlio gave a too marked overshoot ofν1.The model predicted a too large truncation at long times of the relaxation modulus with increasing magnitude of shear.