[en] Recently, experiments were carried out at Bevalac to detect K^- in heavy-ion (Si-Si) collisions at an incident energy of 2.1 GeV/nucleon. The threshold for K^- production in the nucleon-nucleon collision is approx. 2.5 GeV. The observation of K^- at subthreshold energies in heavy-ion collisions implies that more than one projectile nucleon must be involved in converting their kinetic energies into the mass of K^-. This experiment provides therefore the possibility of studying nuclear collective effects, such as Fermi motions, coherent production, and multiple collisions. Preliminary data can be largely explained by conventional rescattering theory