Ethylene decreases the content of endogenous abscisic acid (ABA) and increases the level of bioactive gibberellin $A_1;(GA_1)$ in the submerged internodes of deepwater rice. During partial submergence, internodes of deepwater rice undergo rapid elongation as a result of ethylene accumulation in the internodal lacunae. In an in vitro experiment using stem sections from deepwater rice, treatment with $5;{mu}L;L^{-1}$ ethylene promoted stem growth by up to 3.2-fold times over air treatment. Expression patterns were analyzed for genes that encode GA- and ABA-biosynthesis enzymes to determine any possible molecular basis for the changes observed in $GA_1$ and ABA contents as a result of ethylene action. Expression of the OsGA20ox2 and OsGA20ox4 genes, which encode GA 20-oxidase, and of the OsGA3ox2 gene, which encodes the enzyme that converts $GA_{20};to;GA_1$, was up-regulated, whereas that of three ABA-biosynthetic genes -- OsNCED1, OsNCED2, and OsNCED5 -- was down-regulated in the presence of ethylene. These results indicate that GA and ABA contribute equally to the submergence- or ethylene-induced stem elongation of deepwater rice via the coordinated and opposite regulation of biosynthesis.