Changes in the rates of ethylene production by Japanese persimmon fruits (Diospiros kaki Thumb. cv. Fuyu) were observed by addition of 1-aminocyclopropane-l-carboxylic acid (ACC) harvested at different atages of development. Intact fruits were vacuum -infiltrated with various concentrations of ACC solution (0, 0.04, 0.2, and 1.0mM) . Imediately after application of ACC ethylene production in all fruits increased. A higher concentration of ACC had an increasingly larger effect. The treatment with 1.0 mM ACC significantly increased the rate of ethylene production above water control, whereas 0.2 mM and 0.04 mM ACC gave a less effect. The effect of ACC application was stronger in younger fruits than in matured ones. Although control fruits at all stages of development had a lag-time of more than 1 hour in production of ethylene, ACC treatment increased ethylene production without a lag. The evidence indicates that Japanese persimmon fruits show the activity of ethylene forming enzyme at any stage of development. It is therefore concluded that a low level of ACC synthase activity may limit the ethylene production in intact fruit.