Knowledge of the hydrological processes in the karst areas of the Apuseni Mountains (Romania) are currently hampered by the limited available information. To partly address this issue, we have investigated the dynamics of stable isotopes in waters of the Ocoale Plateau, central Apuseni Mts. We have collected 103 samples from meteoric water, rivers, springs and caves and analyzed them for their isotopic composition. The data indicates that meteoric waters are the main source for all types of water; however, differences in the duration of underground flow, recharge and residence time occur in relation to the characteristics of the cave systems and external hydrological regime