  We derive target mass corrections (TMC) for the spin-dependent nucleon
structure function g1 and polarization asymmetry A1 in collinear factorization
at leading twist. The TMCs are found to be significant for g1 at large xB, even
at relatively high Q^2 values, but largely cancel in A1. A comparison of TMCs
obtained from collinear factorization and from the operator product expansion
shows that at low Q^2 the corrections drive the proton A1 in opposite
directions.
