  GAIA present day (end-2002) photometric performances, estimated basing on the
stellar populations crucial for understanding the formation and evolution of
the Galaxy, are discussed. Performance of the GAIA photometric systems (PSs) is
evaluated taking into account their ability to simultaneously determine the
main stellar parameters: T_eff, log g, [M/H], and E(B-V), for a large variety
of stars down to V ~ 20. A sample of the stars (Photometric System Test
Targets, PSTTs) applicable for evaluation of the GAIA photometric systems is
presented. Definitions of the 1X PS and its accuracies of stellar
parameterization are given. We conclude that there is still no photometric
system, which would allow to achieve the scientific objectives of the GAIA
mission at the limiting magnitude V=20, proposed to date.
