Structure−property relationships of aligned block copolymer lamellae in the vicinity of theorder−disorder transition are studied by a combination of optical birefringence and rheology. Minimizingdefect density was a crucial part of our experiments. The organization of block copolymer chains intoaligned lamellae leads to a reduction in both zero shear viscosity and compliance relative to the disorderedstate. The frequency dependencies of the storage and loss shear moduli of the aligned lamellae are closeto the Rouse prediction. In addition, the measured value of the compliance of the ordered and alignedstate is within a factor of 2 of the Rouse prediction (agreement obtained with no adjustable parameters).In contrast, large differences between the experiments and the Rouse model are seen in the disorderedstate due to the presence of concentration fluctuations.