Ethylene production was measured in fruit of a number of cling peach cultivars within 1 h of picking. During the period when ethylene production on the tree was rising exponentially, fruit from cultivars with low preharvest drop produced ethylene at much lower rates than fruit from high-drop cultivars. Also, the ethylene peak tended to occur earlier relative to flesh colouring in high-drop cultivars. The level of endogenous ethylene controlled the rate of abscission, which was retarded by holding the fruit in an atmosphere of 15% CO*2. Abscission was accelerated by injection of (2-chloroethyl)- phosphonic acid, but the cultivars Golden Queen and Phillips, and an unnamed cultivar, differed from each other in their sensitivity.