The microhardness (H) technique was recently applied to poly(butylene terephthalate) (PBT) and its multiblock copolymer of poly( ether ester) (PEE) type for examination of the stress-induced polymorphic transition. In the present study, these investigations are extended to blends of PBT and PEE. For this purpose, drawn and annealed with fixed ends at 170 degrees C for 6 h in vacuum bristles of PBT-PEE, blends were characterized with respect to their microhardness at various stages of tensile deformation. H was measured under stress, with each step of deformation amounting 5%. The variation of H with strain (epsilon) shows 2 sharp stepwise decreasing values (by 40%). Each step is defined in a relatively narrow deformation (epsilon) range (2-5%) due to the stress-induced alpha --> beta polymorphic transitions arising in PET crystallites. The first polymorphic transition (at epsilon = 2-3%) is assigned to the PBT crystallites of the homopolymer (homoPBT). The second transition (at epsilon = 25%) is associated to those crystals within the PEE copolymer. From the observation of two distinct transitions, separated by a deformation interval of epsilon = 20% it is concluded that (1) homoPBT and the PET segments from PEE crystallize separately (no cocrystallization takes place), and (2) the 2 species of PET crystallites are subject to the external mechanical loading, not in a simultaneous manner, but in a two-stage process. In the deformation range between the 2 transitions (epsilon = 2-3% and 25%), it is pointed out that conformational changes are induced through stretching mainly in the amorphous regions.