  We derive in-medium nucleon-nucleon (NN) cross sections in a microscopic
model. Our calculations are based upon the Bonn NN potential and the
Dirac-Brueckner approach for nuclear matter. We consider energies up to 300 MeV
(in the laboratory frame) and densities up to twice nuclear matter density. Our
results deviate substantially from cross section parametrizations that are
commonly used in the nuclear medium.
