[en] This paper deals with the investigation of the performances of the spectrometric systems for measurement of environmental samples. The attention was focused on the determination of Minimum Detectable Activity for various geometries and, specifically, for air particulate samples collected on cellulose filters by an high-volume sampler (up to 20,000 m³/day) and reduced to a square packet-sample geometry, 6 cm wide and 0.7 cm thick. A calibration procedure was experimented by adding a small amount of a radioactive powder to the sample matrix. In this way matrix self-absorption effects are intrinsically taken into account for each energy considered. Detection efficiency calibration was performed also for Marinelli beakers, well-suited for low-level activity measurement in large volume samples. The spectra detected on some environmental matrices have allowed evaluating very low activity concentration with a simple measurement technique, easily adoptable also in routine analyses.The spectrometric analyses performed on various environmental samples demonstrate the utility of low-level spectrometric systems, even situated at ground-level. The choice of a proper detector, with high radioactive purity and electronic components placed next the dewar, besides the selection of shielding materials, allows the determination of weak activity concentration with a good accuracy. The low detection limits reached with those spectrometric systems and the absence of significant photo peaks in the background spectra, detected for many days, allow the determination of activity concentration without incurring in complex stripping calculations of background photopeak components. Furthermore, efficiency calibration with the use of an homemade standard, previously calibrated by comparison with a commercial standard source, permits to take intrinsically into account self-absorption effects. At the present, L.E.P.S. (low energy photons spectrometer) is used to the daily determination of ²¹⁰Pb air concentration while the other HP Ge system is employed within the framework of an environmental surveillance program. (N.C.)