Polymer single crystals or lamellae are widely used in models for more complex systems such as fibers, films, or bulk polymer. Determination of important thermodynamic and physical properties for the crystals is often frustrated by their tendency to reorganize on heating. Partly as a consequence of this, the melting ranges for high molecular weight polymers are often quite broad. A novel technique has been developed which permits a more detailed examination of the melting/morphology relationships that exist in single crystals. This has led to the observation that high molecular weight polyethylene (PE) single crystals possess much narrower melting ranges than had been previously reported. It has been possible to determine distinct transformation temperatures for the {100} and {110} fold sectors that exist in some PE crystals. Melting point determinations have been made on a series of isothermally crystallized PE crystals using DTA. Narrow multiple peaked thermograms were obtained, and peak position and ratio could be related to morphological differences between the crystals.