The rotational response of the Earth to Pleistocene deglaciation is studied by means of a multilayered, viscoelastic Earth model based on the preliminary reference Earth model (PREM). Incompressible viscoelastic deformation is evaluated from a self-compressed initial state. The novelty of our approach stands on the application of a fully analytical normal mode theory to the response of the Earth to surface loads and variations in the centrifugal potential for large numbers of viscoelastic layers, as requested by PREM. Assuming that both present-day true polar wander (TPW) and changes in the second-degree component of the geopotential (J˙2) are solely due to Pleistocene postglacial rebound, we obtain for a two-layer viscosity model that the upper mantle viscosity must be lowered to about 1--5¿1020 Pa s with respect to the classical value of 1021 Pa s. This upper mantle viscosity is accompanied by an increase of the lower mantle viscosity by a factor of 25, in agreement with some recent relative sealevel (RSL) data analyses and convectively supported long-wavelength geoid anomalies. When the viscosity contrast is located at 1470 km depth, TPW and J˙2 require a viscosity of 1021 Pa s in the upper part of the mantle (above 1470 km depth), with a moderate viscosity increase in the lowermost portion of the mantle. This result indicates that a viscosity of 1021 Pa s is appropriate for a wider portion of the mantle than the upper mantle, in agreement with Haskell's <1935> estimate that was not limited to the seismically inferred 670 km boundary. ¿ 1997 American Geophysical Union