A method for characterization of paracrystalline structures in ethylene-propylene copolymers is proposed, based on classical dynamic mechanical measurements performed at different temperatures and frequencies, and on a particular analysis of the resulting modified Cole-Cole plots. A collapse function relative to the disappearance of all ordered structures is evaluated, from which the differential distribution of mechanically effective constraints in the polymer samples may be obtained. At each temperature the total amount of ordered structures present appears to be determined by copolymer compositions and microstructure, and not by thermal treatments. The contribution of paracrystalline structures is revealed from the comparison of the mechanically effective distribution functions with the calorimetric crystalline transitions in the same sample. (C) 2003 Published by Elsevier Ltd.