I. Stanev, S. Vesselinov. Hydrogeothermal conditions of Northwest Bulgaria. The hydrogeothermal conditions of the main thermal water-bearing horizons in Northwest Bulgaria are considered. Besides the hydrogeothermal maps compiled and the description of the thermal water-bearing horizons, a criterion is established which is used for determination the boundary between recent infiltration water-bearing systems and elision ones on the one hand, and on the other hand – with postelision water-bearing systems of the Moesian and Gethian artesian basins. A space distribution of the natural water-bearing and thermal water-bearing systems is made on the basis of these hydrothermal studies. The vertical and horizontal zonality of the above systems is also studied.