  Optimum nuclear parton distributions are determined by an analysis of muon
and electron deep inelastic scattering data. Assuming simple A dependence and
polynomial functions of x and 1-x for nuclear modification of parton
distributions, we determine the initial distributions by a chi^2 analysis.
Although valence-quark distributions are relatively well determined except for
the small-x region, antiquark distributions cannot be fixed at medium and large
x. It is also difficult to fix gluon distributions.
