Conceptual hydrological model HBV is extensively used in operational hydrological forecasting and water balance studies. In this paper, we apply the HBV model on 190 km2 basin Bolska. Using the tools of Monte Carlo simulation, which is built in the HBV-light model, we analyzed the individual sensitivity of the parameters, a sensitivity by changing the two parameters and the influence of parameters on the maximum flow in the flood. Analysis were done on the basis of Nash-Sutcliffe model efficiency coefficient. Individual analysis showed greater sensitivity of response routine parameters with respect to other three routines; it is most clearly seen through the influence of the middle box outflow and lower box outflow on the total runoff. Parameters of the snow routine have proved to be insensitive. By varying two parameters simultaneously the sensitivity analysis revealed interdependence of parameters in most of parameter combinations, reflecting the uncertainty in the results. Parameters that showed the most
influence on the maximum flow are: K0, K1, UZL, PERC and FC.