CO2 (40, 200, 400 loM) was added to the root systém of 10-d-old pea plants (Pisum sativum L. cv. Ran). The Co2'''-excess caused a reduction in the plant fresh and diy masses and water and chlorophyll contents. The rates of photosynthesis and transpiration decreased, while proline content and stomata resistance increased. The dramatic effect of Co2+-toxicity was expressed both in an inhibition of ribulose 1,5- bisphosphate (RuBP) carboxylase activity and a stimulation of RuBP-oxygenase and phosphoenolpyruvate carboxylase activities on the 4‘h day of cnltivation of plants in a solution of 400 pM C6^*.