Measurements of atmospheric carbon dioxide were made on the NCAR C-130 aircraft during the ACE-1 program. The objective of the CO2 measurements was to use them as an aid in tracing airmass history. In the main ACE-1 research area, the South Tasman sea, west of the Island of Tasmania, the vertical concentration profiles of CO2 were quite consistent, with a concentration of about 359 ppmv near the ocean surface and increasing by about 1-3 ppmv at 6000 m. Flights downwind of Tasmania show reduced CO2 concentrations due to the removal of CO2 by vegetation. Details of the CO2 measurements for several flights will be discussed. The National Center for Atmospheric Research is sponsored by the National Science Foundation.