Enthalpy measurements by means of solution microcalorimetry were obtained on a PVC resin in the temperature range 37-110°C. Enthalpy measurements above Tgdetect a heat of fusion of about 1.5 cal/g of polymer and thereby demonstrate the presence of a soluble ordered structure in PVC. Enthalpy measurements on samples quenched and slow-cooled from within the temperature interval 37-220°C confirm the value of 1.5 cal/g for the heat of fusion as well as demonstrate a broad melting range of 130-200°C.