The presence of very low concentrations of ethylene had dramatic effects on the opening of cut flowers of rose (Rosa hybrida L.). Depending on cultivar, the rate of opening was unaffected (e.g., ‘Gold Rush’), accelerated (e.g., ‘Sterling Silver’), or inhibited (e.g., ‘Lovely Girl’). The K m for the inhibition of opening of ‘Lovely Girl’ by ethylene was 4 ppb. Flowers of some cultivars (e.g., ‘Royalty’) had an abnormal shape when opened in the presence of ethylene. The effects of exogenous ethylene could be overcome by pretreatment of the flowers with 0.5 μmol silver thiosulfate per stem. No phytotoxicity was observed in flowers treated with 2 μmol per stem. Examination of the kinetics of the ethylene/Ag+ interaction in inhibition of opening of ‘Lovely Girl’ flowers indicated that the Ag+/ethylene interaction was competitive.