The dynamic mechanical behaviour of miscible, amorphous blends of poly(ether ether ketone) (PEEK) and poly(etherimide) (PEI) was studied over a wide temperature range incorporating the cu transition and sub-T-g transitions. The segmental motions responsible for the cu process were significantly slowed by blending and were dominated by PEI. Fits of the data to the Kohlrausch-Williams-Watts function showed increased broadening in the blends, arising from concentration fluctuations, and a reduction in the mechanical relaxation strength. The temperature dependence of the WLF shift factors, obtained from cooperativity plots, did not correlate with the stretched exponential broadness parameter in the manner predicted by the coupling model. Two sub-T-g transitions in PEI and the blends, and one in PEEK, were detected. The PEI beta transition, which occurred around 100 degrees C at 1 Hz, was strongly affected by the presence of PEEK. The blend gamma transition shifts its temperature position with composition in a linear manner between the PEEK beta transition (-69 degrees C at 1 Hz) and the PEI gamma transition (-81 degrees C at 1 Hz).