The fusion behavior of lightly cross-linked polyethylene films isothermally crystallized at various temperatures and extensions has been examinedonadifferential scanning calorimeter (DSC). Ameans to hold the specimen at fixed elongation during the melting was devised. At large extensions, a separate higher-temperature endotherm was observed in addition to the major peak, indicating a two-phase nature of the crystal morphology. In addition, crystallization experiments performed on the DSC show the crystallization process to consist of two stages. In contrast to reported results for natural rubber and polychloroprene, the melting temperature for polyethylene was not found to be strongly dependent on crystallization temperature or extension. The reason for the differences between polymers is not presently understood, but they may reflect variations in morphological details.