Sunflower seedlings (Helianthus annuus hybrid Select) were grown in a complete nutrient solution in the absence or presence of Cd2+ (10 and 20 μM). Analyses were performed to establish whether there was a differential effect of Cd2+ on mature and young leaves. After 7 d the growth parameters as well as the leaf area had decreased in both mature and young leaves. Accumulation of Cd2+ in the roots exceeded that in the shoots. Seedlings treated with Cd2+ exhibited reduced contents of chlorophyll and CO2 assimilation rate, with a greater decrease in young leaves. The photochemical efficiency of photosystem II (PSII) was not altered by Cd2+ treatment in either mature or young leaves, although during steady-state photosynthesis in young leaves there was a significant alteration in the following parameters: quantum yield of electron transport by PSII (ΦPSII), photochemical quenching (qP), non-photochemical quenching (qNP), and excitation capture efficiency of PSII (Φexc).