  We discuss the possibility of a direct access to transversity distributions
by measuring the double transverse spin asymmetry A_TT in p pbar --> J/Psi + X
--> l^- l^+ + X processes at future GSI-HESR experiments with polarized protons
and anti-protons. In the J/Psi resonance production region, with 30 < s < 45
GeV^2, both the cross-section and A_TT are expected to be sufficiently large to
allow a measurement of h_1^q(x,M^2); numerical estimates are given.
