Available experimental data of shearing flows are used to test the BKZ fluid model. The strain‐energy function is assumed in the form ofU=M(s)g(I1, I2),whereM(s)is obtained from the small‐amplitude oscillatory shearing data. The functionF=2(∂g/∂I1)+2(∂g/∂I2)is then calculated from simple shearing data (either shear stress or first normal stress difference). Nonuniqueness ofFis seen in the results and it is suggested that the BKZ fluid model can be used only up to moderate shear rates. The stress growth after the start of simple shearing is also predicted and compared with experimental data. The prediction of stress relaxation after the cessation of simple shearing is also made and is qualitatively in agreement with experimental data.