The diurnal changes in leaf net photosynthetic rate (PN) and sugar and nitrogen contents in wheat [Triticum aestivum (L.) cv. HD 2285] and mungbean [Vigna radiata (L.) Wilczek cv. PS 16] were analysed under ambient, AC [350±25 µmol mol-1] and elevated, EC [600±50 µmol mol-1] CO2 concentrations. In both mungbean and wheat PN of AC- and EC-grown plants compared at the same CO2 concentration showed that PN was higher under EC. However, increased PN in EC-plants declined in the afternoon and approached PN of AC-plants. Depression in PN, however, was less in mungbean compared with the large depression in wheat. Greater down regulation of PN in wheat was associated with the accumulation of large amount of sugars and low nitrogen content in wheat leaves. Mungbean leaves accumulated mostly starch under EC and the difference in N content in AC- and EC-plants was relatively less than in wheat. and A. C. Srivastava ... [et al.].