The role of endogenous ethylene during germination of non‐dormant seeds ofAmaranthus caudatusL. was investigated. The seeds readily germinated in water and darkness at 24°C. Application of ethylene or of its precursor I‐aminocyclopropane‐I‐carboxylic acid (ACC) slightly increased the rate of germination. Both compounds effectively antagonized osmotic inhibition by polyethyleneglycol. Application of aminoethoxyvinylglycine (AVG) reduced ethylene production by 90% but did not inhibit germination. However, germination was inhibited by 2,5‐norbornadiene, a competitive inhibitor of ethylene action. This inhibition was counteracted by ethylene, ethephon or ACC and enforced by AVG. It is concluded that the action of endogenous ethylene is an indispensable factor during germination of non‐dormant seeds ofA. caudatus.Ethylene action is required from the start of imbibition on. In water, low levels of endogenous ethylene are sufficient for this action. PEG increased the ethylene requirement