  We review the present data on high-energy, spin-dependent photoabsorption. We
find a strong isotriplet term in $(\sigma_A - \sigma_P)$ which persists from
$Q^2 \sim 0.25$GeV$^2$ to high $Q^2$ polarised deep inelastic scattering. For
$Q^2 \sim 4$GeV$^2$ and $x$ between 0.01 and 0.12 the isotriplet part of $g_1$
behaves as $g_1^{(p-n)} \sim x^{-{1 \over 2}}$, in contrast to soft Regge
theory which predicts that $g_1^{(p-n)}$ should converge as $x \to 0$. The
isotriplet, polarised structure function $2x g_1^{(p-n)}$ is significantly
greater than the isotriplet, unpolarised structure function $F_2^{(p-n)}$ in
this kinematic region. We analyse the low $Q^2$ photoabsorption data from E-143
and SMC and use this data to estimate the high-energy Regge contribution to the
Drell-Hearn-Gerasimov sum-rule.
