The universal calibration of gel permeation chromatography presents deviations when star-shaped polymers are used, especially when they present high segment density. Polymers presenting high segment density also have higher values of Flory's parameter (D than the corresponding flexible, linear polymers. This deviation disappears if we express the hydrodynamic volume of the polymers with the quantity [eta]M/Phi (where [eta] is the intrinsic viscosity and M is the molecular mass) instead of the commonly used quantity [eta]M. (c) 2005 Wiley Periodicals, Inc.