The gaseous plant hormone ethylene affects somatic embryogenesis in various ways depending on the species or explants used. Inclusion of ethylene action inhibitors, namely silver ions in culture media increased somatic embryogenesis in some species. Large scale (bioreactor) yields of somatic embryos were less than these from flask cultures. Ethylene depletion from the bioreactors due to aeration is considered as a possible reason for the decrease in somatic embryogenesis. Ethylene is discussed as a physiological marker related to embryogenic potential. Wound ethylene evolved after transformation experiments might have some inhibitory role on transformation but results are contradictory. Ethylene plays different roles in long term storage (low and ambient temperatures) of embryogenic cultures. Use of transgenic technology in ethylene biosynthesis reduction is discussed as a way to understanding ethylene role in somatic embryogenesis.