A cDNA homologous to the ethylene-response sensors (ERS/ETR1) from Arabidopsis thaliana was isolated from a Rumex palustris cDNA library. This cDNA, RP-ERS1, was 2421 bp long and shared 66% nucleotide homology with ETR1 and ERS in their coding regions. The transcript level of RP-ERS1 was actively regulated during the leafelongation response of R. palustris upon flooding. RP-ERS1 transcript levels increased after submergence, and also after exposure to high concentrations of ethylene and carbon dioxide and low concentrations of oxygen. These results suggest that R. palustris plants may respond to flooding stress by increasing the number of their ethylene receptors.