The spin-dependent cross sections for semi-inclusive lepton-nucleon
scattering are derived in the framework of collinear factorization,
including the effects of masses of the target and produced hadron
at finite momentum transfer squared Q^2.
At leading order the cross sections factorize into products of
parton distribution and fragmentation functions evaluated in terms
of new, mass-dependent scaling variables.
The size of the hadron mass corrections is estimated at kinematics
relevant for future experiments.