The effects of elevated atmospheric carbon dioxide on the growth and development of celery (Apium graveolens) were examined to determine if anticipated global increases in CO2 will affect the nutritional quality and secondary chemistry of celery. The size (fresh and dry mass), nitrogen and carbon composition, and concentrations of linear furanocoumarins of celery grown under ambient (363 uL/L) and elevated (718 uL/L) carbon dioxide were analyzed. Growth under elevated CO2 resulted in larger petioles, reduced nitrogen content, and higher C:N ratios in both leaves and petioles. However, CO2 treatment did not affect plant water content or carbon content. Moreover, in contrast to the carbon-nutrient balance hypothesis, the increased C:N ratios of plants grown under elevated CO2 were not associated with increased concentrations of potentially harmful linear furanocoumarins. Levels of linear furanocourmarins in the petioles of plants from each treatment did not exceed concentrations reported to cause acute or chron ic contact dermatitis.