Effects of preheating temperature on energy consumption,fibre collapse and pulp quality in refining of spruce TMP reject material were studied. At preheating to temperatures well above the softening temperature of lignin thick-walled fibres were collapsed to a higher degree. Shives and fibres in the BMN +10 fraction were efficiently reduced. An increase in sheet density was obtained. Energy consumption was reduced, at a certain freeness level. This study indicates that an improved surface smoothness can be achieved as result of high temperature reject refining.