Cotton plants were grown in late spring under full sunlight in glasshouses containing normal ambient partial pressure of CO2 (32 _+ 2 Pa) and enriched partial pressure of CO2 (64 _ 1.5 Pa) and at four levels of nitrogen nutrition. Thirty-five days after planting, the total dry weights of high CO2-grown plants were 2to 3.5-fold greater than plants grown in normal ambient CO2 partial pressure. Depending on nitrogen nutrition level, non-structural carbohydrate content (mainly starch) in the leaves of plants grown in normal CO2 was between 4 and 37% of the total leaf dry weight compared to 39 to 52% in the leaves of high CO2-grown plants. Specific leaf weight calculated using total dry weight was 1.6-to 2-fold greater than that based on structural dry weight. In high CO2-grown plants the amount of non-structural carbohydrate translocated from the leaves at night was between 10 and 20% of the level at the end of the photoperiod. This suggests that the plant was unable to utilize all the carbohydrate it assimilated in elevated CO2 atmosphere. While there was a 1.5-fold enhancement in the rate of CO2 assimilation in plants grown in 64 Pa CO2, there was, however, some evidence to suggest that the activities of other metabolic pathways in the plants were not stimulated to the same extent by the enriched CO2 atmosphere. This resulted in massive accumulation of non-structural carbohydrate, particularly at low level of nitrogen nutrition.