The effect of preliminary thermomechanical treatment on the strength, elongation, hardness, X-ray line broadening, and prior austenite grain size of D6AC steel has been investigated. In this type of treatment the deformation is performed prior to austenitizing, and rapid rate heating to the austenitizing temperature must be used. The response to preliminary thermomechanical treatment was determined as a function of prior structure, amount of prior deformation, austenitizing temperature and time, preaustenitizing heat treatment, and tempering temperature. Thus far, the yield strength has been increased about 25 pct along with a significant increase in tensile elongation for some tempering temperatures. The tensile strength, however, remains essentially constant. A comparison of the X-ray line broadening and yield strength measurements indicates that these parameters are being influenced by the same structural changes. The results are explained on the basis of a retention of the work hardened structure (introduced during the prior deformation) through the austenite and martensite transformations.