Hydrological background of the dune slack vegetation in the Kiskunság In the southern Kiskunság the natural vegetation (sand steppe, fen meadow, fen or marsh and alkali vegetation) survived in the dune slack meadows (DSM). The vegetation of these meadows are species rich, and has high natural value. The main goal of this study is to reveal the hydrological backgrounds in order to help conservation of the natural values. Two DSM was investigated (MM and CS site): vegetation was sampled, observation wells were planted, and data of other wells in similar position were used to describe the hydrological background of the vegetation. The characteristic groundwater level of the same vegetation type in the relatively wet 2005 year was higher in MM site, than in the CS site. We suppose, that this is a consequence of the earlier vegetation change because of the strong decrease of groundwater level in the region of MM site. The model of hydraulic flow system showed that the DSMs are situated in hydraulic discharge zones. We suppose, that an upward flow plays an important role in development of alkali vegetation in the CS site. Cross-correlation coefficient between groundwater and previous precipitation indicated a quick infiltration of rainwater into the soil, and a pressure front of the groundwater stream reaching the area of well after 22-23 days after rainfall. The quick and strong regional hydrological changes, especially the decrease of groundwater level would endanger this valuable vegetation, but certain resistance and plasticity of it is rather possible.