Elevated carbon dioxide levels may be increasing the transfer of carbon from the atmosphere to soil. To test this CO2 fertilization hypothesis, we collected soil cores from the Free-Air Carbon-Enrichment (FACE) facility in the Duke forest in 1996 and 2000. CO2 fertilization occurs when elevated carbon dioxide levels enhance plant growth. Preliminary results show that the elevated rings accumulated mineral-bound soil organic carbon twice as fast as the ambient rings. Nitrogen accumulation showed the same trend. There was considerable variability in the CO2 fertilization response, which may be related to the availability of phosphorous in the soil at the FACE site. The response of this forest to elevated atmospheric carbon dioxide levels suggests that CO2 fertilization may be increasing soil carbon storage in similar closed-canopy forests and slowing the build-up of atmospheric carbon dioxide.