Two values, unity and 4/3, of the dilution exponent alpha in the Milner-McLeish dynamic dilution theory for relaxation of entangled polymers are tested thoroughly against experimental data for linear, star, and star-linear blends of 1,4-polybutadiene using the same set of values for the parameters: the plateau modulus G(N)(0), the entanglement spacing Me, and the equilibrium time tau(e), for-each alpha. We find that alpha = 4/3 gives good agreement with all data sets using the literature value for the plateau modulus and an entanglement spacing that is very close to the value calculated from the plateau modulus. While we can also predict linear and star polymer rheology with adjusted Me and tau(e) for alpha = 1, the required value of Me is 40% higher than the one calculated from the plateau modulus. (C) 2003 The Society of Rheology.