  After reviewing QCD definitions of the chiral-odd spin-dependent parton
distributions $h_1(x,Q^2)$ and h_L(x,Q^2), I will summarize the main feature of
the recent two results in perturbative QCD: (i) Next-to-leading order $Q^2$
evolution of h_1(x,Q^2). (ii) Leading order Q^2 evolution of the twist-3
distribution h_L(x,Q^2) and the universal simplification of the Q^2 evolution
of all the twist-3 distributions in the large N_c limit.
