The study of the vadose zone has been based on own continuous long-term measurements and analyses of precipitation on the surface and of several representative trickles in the vadose zone of Postojna Cave over consecutive hydrological years. It offers an explanation of the dynamics of the percolation of water and simultaneous transfer of contaminants and their impact on the dissolution of carbonate rock in the vadose zone. The research contributes to the understanding of the role of the vadose zone in the karst aquifer. The emphasis is placed on a multi-parameter approach based on the simultaneous use of a number of different methods, not only tracing natural tracers (such as the continuos measurement of discharge, temperature, electrical conductivity, isotopic composition of oxigen, content of carbonates, calcium, magnesium, chlorides, nitrates, sulfates and o-phosphates, electrical resistivity imaging) but also tests with artificial tracers using different methods of injection. The research contributes to the understanding of the role of the vadose zone in the karst aquifers and is directly applicable in planning the long-term protection of the quality of karst springs.