  The production and propagation of kaons and antikaons has been studied in
symmetric nucleus-nucleus collisions in the SIS energy range. The ratio of the
excitation functions of K^+ production in Au+Au and C+C collisions increases
with decreasing beam energy. This effect was predicted for a soft nuclear
equation-of-state. In noncentral Au+Au collisions, the K^+ mesons are
preferentially emitted perpendicular to the reaction plane. The K^-/K^+ ratio
from A+A collisions at beam energies which are equivalent with respect to the
threshold is found to be about two orders of magnitude larger than the
corresponding ratio from proton-proton collisions. Both effects are considered
to be experimental signatures for a modification of kaon properties in the
dense nuclear medium.
