Kaon production is studied using a Boltzmann type of equation that takes into account three nucleon collisions. Our approach reproduces fairly well existing p-nucleus data. The importance of cooperative process in subthreshold particle production is suggested in comparison between kaon yields from p and d induced reactions. Kaon production has been proposed 1H ) to study the initial stage of a nucleus nucleus collision_ Indeed, due to their long mean free paths in the nuclear environ ment, kaons could be used as probes of the dense and highly excited system formed during the collision of two nuclei. This is not true, for example, for pions which interact strongly with the nucleus, resulting in losing memory of the initial stage of the collision due to reabsorption and/or rescattering effects. However, there are some problems when one deals with kaon production. The most serious one is that the K-elementary production cross section is not well known either experimentally or theoretically.4) The scarce existing data for the elementary process show discrep ancies between various groups.1),4),5) For example, the proton-proton data at 2.5 GeV differs by a factor of two between two different experimental groups! This fact, of course, makes a comparison between theory and experiment impossible at an absolute level. In fact, changes in the elementary cross section can change the theoretical production in p-nucleus and nucleus-nucleus collisions by a factor 2~4. Another source of uncertainty in the calculations is the unknown Equation Of State (EOS) of nuclear matter. In Ref. 6) it was shown that the kaon yield obtained in nucleus nucleus collisions changes of a factor 2 ~ 3 when the compressibility of the EOS is changed from a soft (200 Me V) to a stiff one. This is due to the different values of compression obtained in the two cases which causes a smaller number of nucleon nucleon (N-N) collisions for the stiff EOS. To avoid this problem one could use a p or a d projectile. For such collisions there is little change in the density. However, the EOS is strongly momentum dependent at relativistic energies. 7 ) The momentum dependence of the EOS may strongly affect the kaon yield even for the proton beams_ 2 ) T4e ambiguities in the elementary process and the nuclear EOS do not change the main result of our work since we are interested in the increase of the kaon yield in d induced reactions compared to p-nucleus collisions. In fact, we find that for the p+12C system the kaon yield is a factor 1000 or more smaller than the yield for the d +12C *) Permanent address: Laboratorio Nazionale del Sud, INFN, viale A. Doria ang. via S. Sofia, 95123