Resonance absorption of the radiation from a parametrically tuned laser permits the remote detection and density measurement of pollutant gases at large ranges with single‐ended systems if topographical features or atmospheric aerosol are used as backscattering means. We have built and demonstrated such a transmitter‐receiver system operating at 2.3 &mgr;m in the infrared. The presence and amount of a CO sample placed at a range of 107 m against a topographical backscattering target was established by the absorption of rotational lines in the first overtone transition. The results indicate a range limit of the present equipment at 1.5 km and a sensitivity in good agreement with predictions based on measured linewidths and cross sections.