Nonlinear viscoelasticity was studied for a polystyrene solution in tricresyl phosphate; molecular weight = 5480 kg mol(-1); concentration = 49 kg m(-3). The longest Rouse relaxation time, tau(R), was estimated by fitting the Rouse theory to dynamic modulus at high frequencies. The Doi-Edwards tube model theory presumes that 2tau(R) is the characteristic time for equilibration of chain contour length; (2tau(R))(-1) is the rate for an extended chain to shrink back to equilibrium. The tau(R) value was much lower than that evaluated with more widely accepted methods. However, the shear stress M and the first normal stress difference (N-1) in the start-up of shear flow with low rate of shear (<(2tau(R))(-1)/5) were consistent with the assumption that the contour length is always at equilibrium value. At high rate of shear (>8(2tau(R))(-1)), the maxima of a and N-1 were located at t = 2tau(R) and 4tau(R), respectively, in accord with the interpretation that 2tau(R) is the characteristic time for chain shrink. The strain-dependent relaxation modulus, G(t, gamma), was also studied. At high magnitudes of shear, gamma = 4 or 5, the ratio G(t, gamma)/G(t, 0) decreased rapidly around t = 2tau(R) and leveled off at t = 20(2tau(R)): the chain shrink process plays the main role in damping but a slower process may also be involved. At gamma = 1 or less, G(t, gamma)/G(t, 0) decreased only at times much longer than 2tau(R). The damping of relaxation modulus involves some secondary process with a characteristic time longer than that of the chain contraction process.