ABSTRACT: As a part of complex hydrogeological investigations in the northern part of the Štiavnické vrchy Mts., the mountain range with Miocene-Quaternary stratovolcano geological structure, 10 streams and outflows from the drainage adits were observed for the period of May, 2002 to October, 2003. Hydrological balance on the observed watersheds was performed using the daily data on discharges, precipitation and air temperatures on 5 rain gauges, resp. 3 climatic stations. Discharges observed on the 3 gauging stations on streams by SHMI were also used. The total area with the observed outflow was 454.777 km2. Potential evapotranspiration was calculated using Thornthwaite’s method, and volume of actual evapotranspiration from spatial altitudinal distribution of rainfall, air temperatures and average soil cover field capacity of 171 mm. Results of this balance showed the role of the major draining element – the gallery in Voznica, as well as the drainage of natural origin, caused by geological structures, to the Jasenica and Neresnica watersheds. We assume that especially hidden groundwater outflow from Krupinica, Klinkovica, Tisovník, Ľubica and Kocanský potok brooks watersheds contribute to the relative richness in water amounts of Jasenica and Neresnica, where investigation drillings in the past discovered major groundwater resources (Podzámčok and Dobrá Niva).