Ethylene evolution in excised apple (Malus domestica Borkh.) spurs was measured following the application of thinning treatments. Within 1 day (20 hours) of application, ethylene evolution by spurs of ‘Golden Delicious’ trees treated with 15 ppm napthaleneacetic acid (NAA) and 100 ppm (2-chloroethyl)phosphonic acid (ethephon) was 5 times greater than in control spurs, and those treated with 200 ppm ethephon evolved seven times more. Less fruit thinning occurred in response to the application of 100 ppm ethephon than 15 ppm NAA. Increased ethylene evolution was also detected in attached ‘Spatbluhender’ fruitlets 8 hours after NAA treatment.