Radionuclide radiation monitors used nowadays can operate fairly well in measuring the parameters of the radiation type for which they are intended and calibrated. However, in many cases (particularly in emergency situations) the detector is exposed at a time to several types of radiation. Under such conditions its readings may be noticeably influenced by concomitant radiation. In view of this fact interpretation of the measurement data is embarrassing. Bearing this in mind, it is advisable that the available monitors be modernized and new ones be devised for mixed radiation with the common equivalent surface thickness amounting to 1 g/cm2 of tissue equivalent substance.