  The rapidity distribution of $\Lambda$ and $\bar{\Lambda}$ produced in
nucleus-nucleus collisions at CERN energies is studied in the framework of an
independent string model - with quark-antiquark as well as diquark-antidiquark
pairs in the nucleon sea. It is shown that, besides the
$\Lambda$-$\bar{\Lambda}$ pair production resulting from the fragmentation of
sea diquarks, final state interactions of co-moving secondaries $\pi + N \to K
+ \Lambda$ and $\pi + \bar{N} \to K + \bar{\Lambda}$ are needed in order to
reproduce the data. Predictions for $Pb$-$Pb$ collisions are presented.
