The activity of oxaloacetate decarboxylase (OAD, EC 4.1.1.3) was studied comparatively in leaves of the common bean (Phaselus vulgaris L.) plants grown under radiation (1,5,10,50,100,200 Qy) and salt (1,5,10,50,100 mM NaCl) stress conditions. The OAD enzyme was found to be more sensitive to stress in plants grown under various doses of radiation compared with those grown under salinity. The activity of OAD, the major enzyme of the pyruvate biosynthesis, increased during the initial period of the plant development and decreased under stress. However, as adaptive processes occur gradually under salt stress, the plant is more tolerant to stress factors. In both cases, occupying one of the central positions in the energy space, OAD plays a key role in the coordination of interconnected metabolic processes and the energy balance of the organism.