Melts of commercial high-density polyethylene ((M) over bar(W) = 36-85 x 10(3)) were subjected to the hydrodynamics of a Haake Rheocord blender at temperatures (T) spanning the normal processing range (190-260 degrees C), far beyond the disappearance of solid crystals at about 140 degrees C. Torque measurements revealed a peculiar dependence on T, including transitions at about 208 degrees C and 227 degrees C, and non-Arrhenius behavior above and below this range. Resemblances to liquid-crystal polymer phenomena are pointed out, and the impact on the melt processing industries is discussed.