Joint inversions of post-glacial rebound-induced secular changes in low degree harmonics of the geopotential and true polar wander (TPW) systematically indicate that the upper mantle viscosity has a value that is considerably smaller than 1021 Pas. The lower mantle viscosity is about one order of magnitude larger than the upper mantle viscosity. Discrepancies in the viscosity profiles inferred from even and odd zonals are likely an indication of recent, unmodeled glacial forcings and/or insufficient precision in the evaluation of the mass loss from Pleistocene ice sheets. The influence of systematic errors in SLR data reduction due to thermal drag on the LAGEOS satellites for the uneven zonals of the geopotential is avoided by making use of the Starlette and Stella satellites to recover the uneven zonals and by considering lumped coefficients for these uneven terms. ¿ 1998 American Geophysical Union