ABSTRACT: In the Olkusz region Pb-Zn ore has been exploited for a few hundred years. Triassic carbonates hosting ore form a fissure-karstic aquifer. Under natural conditions the Triassic aquifer groundwater was good quality water. Deep mine drainage and the resulting changes in groundwater flow directions caused the activation of various pollution sources that have significantly influenced groundwater quality. This paper presents the spatial distribution of nitrates in Pb-Zn mine outflows in the Olkusz region. The most probable sources of nitrogen compounds determined in mine outflows are presented.