Inhibitors of action and synthesis of ethylene (Ag(+), norbornadien, Co(2+)) were able to reduce the level of gamma-aminobutyric acid (Gaba) in rice roots during the development of an anaerobic environment. The inhibitory effect was reversed by the addition of the G protein activator 5'-guanylylimidodiphosphate. Gaba accumulation was modulated by the presence of CO(2) (inhibitor of ethylene action and synthesis) and stimulated by 2-chloroethylphosphonic acid (ethefon). These findings are consistent with a role of ethylene during a low-oxygen stress.