The first measurements of heat capacity of high-density polyethylene have been obtained for melts in the high-temperature region of 180-260 degrees C. A heat-flow twin calorimeter was used. Abrupt transitions are noticed at 212 and 228 degrees C, analogous to transitions seen earlier with rheological and surface tension measurements. Possible explanations for these phenomena are offered. (C) 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012