[en] Products from the stable isotope production project (ICONS) at the Los Alamos Scientific Laboratory (LASL) have had applications in a number of practical problems. Fully deuterated methanes, using ¹²C and ¹³C (mass-20 and -21, respectively), are detectable in the atmosphere at very low concentrations. The detection limits are due to an almost zero background and a distinct mass-spectrometric line. These properties, coupled with long lifetimes in the atmosphere, make the heavy methanes strong candidates for tracers of atmospheric transport and turbulence on regional to global scales. Three field tests have been conducted to assess the feasibility and to demonstrate the desirable properties of heavy methanes as atmospheric tracers. In the first test in May 1974, heavy methane released at the Idaho National Engineering Laboratory (INEL) was sampled and detected in several midwestern cities up to 2500 km downstream. These results agree with trajectories estimated from observed meteorological data. A second experiment, conducted in December 1975 at the Savannah River Plant, compared two heavy methanes with SF₆ and ⁸⁵Kr over a transport distance of 100 km. Increased detail in meteorological support data and ground-level sampling offered options of data interpretation unavailable in the first test. Qualitative patterns of tracer concentrations show good agreement among the four tracers and are verified by the meteorological inputs. The third experiment, performed in April 1977 at INEL, built on the experience of the previous two. Detailed ground-level sampling arrays at 3, 50, and 90 km from the release point were supplemented by aircraft and a crude sampling line across the Continental Divide at 300-km distance. Two new perfluorocarbon tracers were included for comparison