Nuclear modifications to the Drell-Yan dilepton production cross sections i
n p + A and A + A collisions in the leading twist approximation are caused
by nuclear effects in the parton distributions of bound nucleons. For non-i
soscalar nuclei, isospin corrections must also be considered. We calculate
these effects for p + A and Pb + Pb collisions at CERN SPS energies. Our go
al is to place constraints on nuclear effects in sea quark distributions in
the region x greater than or similar to 0.2. We show that the net nuclear
corrections remain small for p + A collisions at E-lab = 450 GeV. However,
in Pb + Pb collisions at E-lab = 158 AGeV, effects of greater than or simil
ar to 20% are predicted at large M. The data collected by the NA50 collabor
ation could thus be used to constrain the nuclear effects in the sea quark
distributions in the region of the EMC effect, x greater than or similar to
0.3.