  The observation of an anomalous jpsi suppression in nucleus-nucleus
collisions is one of the most important results of the SPS heavy-ion program.
An essential ingredient in this result is the determination, obtained by
studying p-A collisions, of effects not related with the formation of a
deconfined medium. These effects are extrapolated to A-A collisions,
determining a reference jpsi yield that is then compared with the measurements.
In this article we investigate the role of parton shadowing on the
determination of such a reference, and we calculate its effect for In-In and
Pb-Pb collisions as a function of rapidity and centrality.
