  We calculate next to leading order QCD corrections to semi-inclusive
polarized deep inelastic scattering and $e^+e^-$ annihilation cross sections
for processes where the polarization of the identified final-state hadron can
also be determined. Using dimensional regularization and the HVBM prescription
for the $\gamma_5$ matrix, we compute corrections for different spin-dependent
observables, both in the $\overline{MS}$ and $\overline{MS_p}$ factorization
schemes, and analyse their structure. In addition to the well known corrections
to polarized parton distributions, we also present those for final-state
polarized fracture functions and polarized fragmentation functions, in a
consistent factorization scheme.
