The effect of spraying triacontanol (Tria) solution (1 g m'^) on •'*C02 fíxation, ribulose-l,5-bisphosphate carboxylase (RuBPC), nitráte reductase (NR) and photosystem (PS) activities in waterlogged Erythrina variegata Lam. was investigated under field conditions. Seedlings exposed to flooding for 10 d showed a significant reduction in •‘♦CO2 fíxation, and in NR, RuBPC and PS2 activities. Electrophoretic analysis of thylakoid polypeptides indicated a significant loss of 47, 43, 33, 25, 23, 17 and 15 kDa polypeptides in flooded seedlings. However, the application of Tria partially ameliorated the effect of flooding and promoted the above activities. The site of flooding injury was at the oxidation site of PS2 prior to the hydroxylamine donating site and perhaps close or after the diphenylcarbazide donating site. The increase in the RuBPC activity in Tria-treated seedlings under flooding correlated well with the changes in CO2 fíxation rate.