Discrepancies between the length of a traditionally defined Kuhn segment length (l(k)) and a bead size estimated from experimental data have been reported in a number of articles. In this work we emphasize that the traditional definition of the Kuhn segment is an oversimplification and the characteristic ratio, C-infinity is not the only parameter that defines a bead size. We show that the dynamic bead size in polystyrene (PS) might be as large as similar to50 monomers, whereas the traditionally defined Kuhn segment is similar to8-10 monomers. It is shown that with 50 monomers (M similar to 5000) as a size of the dynamic bead, one can explain many inconsistencies in the interpretation of compliance and mechanical relaxation data known for low-molecular weight PS. (C) 2004 Wiley Periodicals, Inc.