The viscosity, eta, of solutions of low-density polyethylene (M-w = 162 kg/mol) in ethylene containing 18.4, 22.5, 27.4, and 35.0 wt % polymer, respectively, was measured over a wide range of temperatures, pressures, and shear rates. The equipment used consisted of a high-pressure autoclave in which the solutions were prepared and a rotational viscometer which was operated by a computer. The solution with a polymer concentration of 35 wt % was found to be shear thinning. Due to experimental inaccuracy the shear influence on the viscosity of the mixtures with lower polymer content could not be identified clearly. The zero-shear viscosities show the expected increase of 77 according to the pressure or polymer concentration and a corresponding reduction of 17 as the temperature is increased. The results are consistent with current theories and can be described well by a mathematical expression based on activation energies, and activation volumes, and on exponential growth of eta with a rise in polymer concentration. (C) 2003 The Society of Rheology.