A low-level radiation monitoring system for the continuous detection of gaseous effluents, both at the point of release and at the boundary of nuclear facilities, has been developed. The prototype system can achieve sensitivities on the order of 10-10 µCi/ml for certain noble gas radioisotopes and provide continuous isotopic identification and monitoring. The system also provides the ability to place a sodium iodide [Nal(Tl)] detector in the natural environment unattended for long durations and perform continuous gammaray spectroscopy. A unique calibration technique using clathrates of the various inert gases was utilized in evaluating the system’s detection efficiency and sensitivity. Field testing of the system was successfully conducted at a nuclear power generating station. The system’s limitations were also evaluated and are mainly due to the relatively poor resolution of Nal(Tl) detectors and the complexity of the gamma-ray spectra resulting from the gaseous effluent emitted by nuclear power reactors.