Embryos heat shocked for 20 minutes at 37^oC show trunk-type denticle belts in the head region, though the trunk and tail region are not affected. Embryos treated at the blastoderm stage show defects in head, truck and tail parts. Embryos treated later (stage 6 or later) do not show segmentation defects in a significant proportion of larvae. 38% of larvae treated at or before stage 10 show homeotic transformations of head to trunk identity, most strikingly in the labial segment, where naked cuticle, a prothoracic denticle belt and a T1 beard appear. Not all head structures are suppressed, as maxillary sense organs, cirri and mouth hooks remain. Longer heat shocks cause more extreme transformations of procephalon and maxillary segment occur, though transformation is still not as complete as for the labial segment. In combination with Scr^hs.PG, tsh^hs.PdZ causes more extreme prothoracic transformations in procephalon and maxillary segment than tsh^hs.PdZ alone. tsh^hs.PdZ increases the expressivity of the homeotic transformations caused by Antp^hs.PHTA or Ubx^hs.PG.