  The target mass corrections are calculated for all structure functions of
neutral and charged current deep inelastic scattering in lowest order in the
coupling constant. Representations of the correction to the twist--2 and
twist--3 contributions are derived both in Mellin-$n$ and $x$-space. The impact
of the target mass corrections on the general relations between the twist--2
and twist--3 parts of the structure functions is studied and three new
relations between the twist--3 contributions are derived.
