A rotational rheometer was used to study LDPE and HDPE at 190 degrees C in the oscillation mode with frequency sweep, 0.1-1000 Hz, and in the steady-state flow mode with controlled shear rate, 0.125-125 s(-1), and shear stress, 0.03-20 000 Pa. Zero shear-rate viscosity, yield stress, complex viscosity, complex modulus and its components, elastic modulus and loss modulus, were detd. Steady-state flow measurements at 170-210 degrees C gave the energy of activation of viscous flow for two LDPE types, 43.22 and 45.75, and for two HDPE types, 20.59 and 22.33 kJ/moL The PE close in m. flow rates had close zero shear-rate viscosity and yield stress values.