The relationship between the NMR parameters and the motion of the flux
lines (FL) in high-T-c superconductors are discussed in the light of
recent Y-89 NMR experiments in YBa2Cu3O7. In particular, novel experim
ents involving echo dephasing due to both thermal fluctuations of FL's
and motion driven by pulsed magnetic fields are presented with prelim
inary results.