  We investigate screening effects of the medium on the potential interaction
between two static 'charges' for different models of dense plasmas in the
one-boson exchange approximation. The potential can exhibit an oscillatory
behavior, which is related to the analytic structure of the corresponding boson
propagators in the complex $q$-plane. We have first revisited the one-pion
exchange in a nuclear medium. In addition to Friedel oscillations, which are
associated to branch cuts in the $q$-plane, there appears another oscillatory
component, which arises from a pole on the pion propagator. This pole is
located appart from the axes, giving rise to an oscillating Yukawa-like
potential. Therefore, we call this phenomenon 'Yukawa oscillations'. This
phenomenon does not appear in the Debye component of the QED screened
potential, even if the coupling constant is artificially increased. We have
also studied a model of QCD quark-gluon plasma. In this case, the one-gluon
propagator also shows this kind of poles. At high densities and/or
temperatures, where one expects perturbative QCD to be valid, the pole shifts
towards large momenta.
