  We calculate the A-dependence of open charm and beauty as well as Drell-Yan
pair production cross sections on nuclear targets taking into account the
difference of quark and gluon distributions in free and bound nucleons. The
results are presented for both proton-nucleus and nucleus-nucleus collisions.
For the case of heavy flavour production at comparatively low energies, if
$\sigma \sim A^{\alpha}$, the values of $\alpha$ are slightly higher than
unity. With increasing energy $\alpha$ decreases in all cases and becomes
smaller than unity. We also show $\alpha$ as a function of Feynman-$x$ of the
produced $Q\overline{Q}$ or $l^+l^-$ pair and obtain that it decreases
significantly in the beam fragmentation region. The sensitivity of our results
to the used set of parton distributions is also discussed.
