  The gluon density in nuclei, G^A(x), is poorly constrained at all x from the
current DIS and Drell-Yan data. In this paper, we point out that J/psi
production measured in proton-nucleus collisions at sqrt(s)=38.8 GeV by the
E866 collaboration puts stringent constraints on the x-dependence of the
G^W/G^Be ratio in the x=0.02-0.1 range. The E866 data suggest a rather mild
x-dependence of G^W/G^Be, and consequently tend to favour DS and HKM sets,
rather than the DSg, EKS, and EPS parametrizations which exhibit a large
shadowing and anti-shadowing.
