(1) Lines of Drosophila melanogaster were "laboratory naturally" or artificially selected under five thermal regimes. (2) Hsp70 expression per unit protein after heat hardening and heat-shock resistance with and without prior hardening were measured. (3) Differences between the selection regimes in the responses of these traits suggest that thermal resistance can be changed independently of inducible Hsp70 expression. (4) Adult males had higher survival than females but did not differ in inducible Hsp70 expression per unit protein after heat hardening. (5) Larvae expressed less Hsp70 per unit protein than adults after heat hardening.