The endotherms of vacuum-irradiated drawn high density polyethylene samples are presented along with the heats of fusion and melting temperatures associated with the first and second melting. Also presented are the shrinkage curves at elevated temperatures. Following are the principal observations and conclusions: 1. (1) For the unirradiated drawn HDPE samples, thickening or reorganization of the long period fibrous material takes place during the DSC measurement. Thus, the sharp unimodal endotherms with high melting points observed for these samples are not truly representative of the actual endotherms. 2. (2) With the vacuum-irradiated drawn HDPE samples, multiple peaks are observed and the melting temperature associated with the main peak is lower; also the endotherms are much broader than those of the unirradiated samples. Because radiation-induced crosslinking inhibits recrystallization following melting, the observed endotherms for the irradiated samples are more exact representations of the actual endotherms of the unirradiated drawn HDPE. These results lead to new information about the microscopic fibrous structure of drawn HDPE.