  The proposed global astrometry mission {\it GAIA}, recently recommended
within the context of ESA's Horizon 2000 Plus long-term scientific program,
appears capable of surveying the solar neighborhood within $\sim$ 200 pc for
the astrometric signatures of planets around stars down to the magnitude limit
of $V$=17 mag, which includes late M dwarfs at 100 pc. Realistic end-to-end
simulations of the GAIA global astrometric measurements have yielded first
quantitative estimates of the sensitivity to planetary perturbations and of the
ability to measure their orbital parameters. Single Jupiter-mass planets around
normal solar-type stars appear detectable up to 150 pc ($V\le $12 mag) with
probabilities $\ge$ 50 per cent for orbital periods between $\sim$2.5 and
$\sim$8 years, and their orbital parameters measured with better than 30 per
cent accuracy to about 100 pc. Jupiter-like objects (same mass and period as
our giant planet) are found with similar probabilities up to 100 pc.These first
experiments indicate that the {\it GAIA} results would constitute an important
addition to those which will come from the other ongoing and planned
planet-search programs. These data combined would provide a formidable testing
ground on which to confront theories of planetary formation and evolution.
