The microstructure of directionally solidified Rene 80 ( DS Rene 80) superalloy in the standard solution heat treated condition was examined. Sub- solidus incipient melting was observed, which was found to be caused by the liquation of terminal solidification reaction products present in front of the gamma - gamma' eutectic in the as-cast alloy. Based on the differential scanning calorimetry ( DSC) measurements, and microstructural examination of heat- treated and water- quenched specimens, sub- solidus incipient melting in the alloy is likely to occur below 1,160 degrees C, and this is a key factor to be considered in the development of a suitable solution heat treatment scheme for DS Rene 80.