Measurements of crystal uplift from bedrock around the edges of Antarctica or Greenland could help constrain the mass balance of those ice caps. Present-day changes in ice could cause vertical displacement rates of several mm/yr around Antarctica and up to 10--15 mm/yr around Greenland. Horizontal displacement rates are likely to be about 1/3 the vertical rates. The viscoelastic response of the earth to past changes in ice could cause uplift rates that are several times larger. By measuring both gravity and vertical displacements, it is possible to remove the viscoelastic effects, so that the observations can be used to constrain present-day thickness changes. ¿ American Geophysical Union 1995