[en] The performance characteristics of two types of passive radon monitors were studied by exposing them in the Paul Scherrer Institute (PSI) radon chamber. The monitors were bare LR-115 and Karlsruhe cup type radon samplers. The exposures were performed at 20^oC and relative humidity of 50% for three different radon levels of approximately 40, 450 and 900 kBq.h.m^-3, respectively. At low exposures, the agreement between the radon concentrations measured by these two monitors with those of the Lucas cell of the chamber monitoring system is to within the statistical error of about ±20%. For the higher radon exposure of 900 kBq.h.m^-3, the results of the cup type and bare monitors show a decrease of ∼15% and ∼37%, respectively, compared with the concentrations measured by the Lucas cell. The results of the experiment carried out at 20^oC and a relative humidity of 90% with the radon exposure level of ∼450 kBq.h.m^-3 showed no appreciable decrease in the measured radon concentrations by the bare and cup type monitors. (Author)