Endogenous 1-aminocyclopropane-1-carboxylic acid (ACC) levels, and the ACC → ethylene (C 2H 4) conversion of exogenously applied ACC in naturally senescing and silver thiosulphate (STS) pre-treated cut carnations, were investigated. Under natural conditions, increase in ACC accumulation coincided with the onset of the climacteric rise in C 2H 4 production. Flowers pre-treated with STS did not show this increase in ACC content. Exogenously applied ACC caused wilting within 24 h and an increase in C 2H 4 production up to 1300 nl/h/flower. Flowers successively treated with STS and ACC produced C 2H 4 at quantities much higher than the controls, but showed no wilting. Together, these data suggest that the binding of C 2H 4 to its receptor leads to an increase in the production of ACC and of C 2H 4. By blocking the C 2H 4 action, the silver ion inhibits the autocatalytic increase in C 2H 4 and the accompanying rise in ACC content.