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.
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