Stress relaxation measurements for large step strains were performed in shear and biaxial extension using an entangled monodisperse polystyrene melt. The shear and biaxial damping functions were obtained, which agreed very well with our previous data for other monodisperse polystyrene melts. The applicability of the Mead, Larson and Doi (MLD) model to the nonlinear damping behavior was investigated based on these experimental data as well as on the previous data of the uniaxial damping function. The experimental data of shear and uniaxial damping functions were larger than the MLD prediction and were closer to the prediction of the Doi-Edwards model with the independent alignment approximation. On the other hand, the experimental biaxial damping function agreed very well with the MLD prediction. The convective constraint release (CCR) accelerates the orientation relaxation when the stretched chain contracts and the CCR gives stronger strain dependence for the damping functions in shear, uniaxial and biaxial extensions. It is suggested that the orientation relaxation time tau(t) around the contraction time predicted by the MLD model may be too short, at least in shear deformation. (C) 2003 The Society of Rheology.