Genetic studies have identified the membrane protein EIN2 (ethylene insensitive 2) as a central component of ethylene signalling in Arabidopsis. In addition, EIN2 might take part in multiple hormone signalling pathways and in response to pathogens as demonstrated by recent genetic and biochemical studies. Here we show, by an integrated approach using in vivo and in vitro fluorescence techniques, that EIN2 is localized at the ER (endoplasmic reticulum) membrane where it shows specific interaction with the ethylene receptor protein ETR1.