Two mercury mining regions from the NW Dinarides are compared with respect to their impact on related drainage basins (of Soca and Kupa Rivers). Stream sediments of the rivers Idrijca, Baca and Soca, which drain the area around world-class mercury ore deposit in Idrija (Slovenia), as well as those from the Cabranka and Kupa Rivers, that drain the area around a smaller Hg-only deposit at Trsce near Cabar (Croatia) have been studied, by detailed mineralogical, chemical and geostatistical studies.|According, to the results, the Idrijca River is highly contaminated with several toxic elements in the town of Idrija. Concentrations (in ppm = mg/kg) were determined in fractions < 63 mu m and 63 - 500 mu m respectively: Hg (9000 and 65000), As (16 and 19.5), Cr (40 and 91), Cu (380 and 113), Pb (55 and 2940). Contamination with Ha, As and Pb persists in downstream Idrijca, as well as in Soca downstream from the confluence with Idrijca. Concentrations of some other trace elements (Zn, Ba, Ni, Cr, Co and Cu) increase in seaward direction. In Soca River drainage basin it was found that in the fraction < 63 mu m Hg shows significant correlation with S, Zn, As, Cu, Sn, U, Mo, W and Sb. In the fraction 63 - 500 mu m significant correlation of Hg was found with S, Fe, Zn, Ni, Pb, Cr, As, Cu, Sn, Zr, Mo, Cd, Sb, Tl and Bi.|On the contrary, in the Kupa drainage basin, the closed Hg-mine in Trsce had only a minor effect on stream sediments. The highest measured concentration of Hg (206 ppb = mu g/kg) was determined at the confluence of Kupa and Cabranka Rivers. Significant correlation of Her (in the fraction < 63 mu m) was found with Zn, Pb, Cu, Au, Li and Cd. The geochemical baseline for Hg in Kupa drainage basin was determined for the first time as 86.1 +/- 47.3 ppb = mu g/kg. With respect to Hg, the basin shows characteristics of a very clean system.