The possibility that prehistoric peoples employed heat treatment of chert and flint as an integral part of their lithic tool production technology is a matter that has long been debated. While previous thermoluminescence (TL) investigations of the heating phenomenon concentrate on finished artifacts, this study investigated the TL stored in biface retouch flakes which are an abundant by-product of the Palaeoindian fluted point manufacture. Examined 175 retouch flakes from three excavated squares at the Parkhill Palaeoindian site, which were then compared with their relatively distant geological source. Accidental heating does not satisfactorily explain the fact that the overwhelming majority of the flakes appear to have been heated. It is concluded that chert heating at this archaeological site was purposeful.