Leaf proteins from Arabidopsis thaliana Landsberg erecta treated with gibberellin A₃ and different light regimes (continuous light, 16/8 h dark/light cycle and 8/16 h dark/light cycle) were analysed by two-dimensional gel electrophoresis. Qualitative differences between the controls and the treated plants were found, indicating that these treatments were responsible for the synthesis of specific proteins. A 35 kDa polypeptide is induced by gibberellin A₃ application and a 25 kDa polypeptide depends on the photoperiod.