  We discuss the crossover from the quantum critical, $z\!=\!1$, to the quantum
disordered regime in high-T$_c$ materials in relation to the experimental data
on the nuclear relaxation, bulk susceptibility, and inelastic neutron
scattering. In our scenario, the spin excitations develop a gap
$\Delta\!\sim\!1/\xi$ well above T$_c$, which is supplemented by the
quasiparticle gap below T$_c$. The above experiments yield consistent estimates
for the value of the spin gap, which increases as the correlation length
decreases.

Condensed Matter