ABSTRACT By means of borings in lœss at Hermies (Pas-de-Calais), two Middle Palaeolithic-dwelling levels have been discovered. The lower level, laying at the top of a gravel surface, is dated from Early Weichselian. The upper level, later than the Early Glacial humic soils, has displayed a Le- valloisian specialized flint workshop, which the state of preservation, similar to Upper Palaeolithic settlements in the open of the Bassin parisien, allows the hope of reaching the scale of event for the prehistory of this time. The uniqueness of activity prooves a real space-organization by the Mousterians during the beginning of Pleniglacial Weichselian.RÉSUMÉ A la faveur de sondages dans des lœss à Hermies (Pas-de-Calais) deux niveaux d'occupation...