Translocation of l4C-sucrose from leaf to fruit was measured in ‘Golden Delicious’ and ‘Staymared’ apple (Malus domestica Borkh.) and ‘Redhaven’ peach (Prunus persica (L.) Batsch) following the application of compounds reported to influence fruitlet abscission. Succinic acid-2,2-dimethylhydrazide (daminozide) reduced 14C translocation in both apple cultivars but reduced fruit set only in ‘Golden Delicious’. Ethephon reduced 14C translocation and fruit set of peach. Abscisic acid (ABA) and 2,4-dinitrophenol (DNP) reduced 14C-sucrose translocation in apple. Enclosing apple limbs in black cloth bags reduced fruit set and naphthaleneacetic acid (NAA) increased leaf water potential. One method of preliminary screening of compounds for apple fruit thinning may be based on their effect on 14C-sucrose translocation from foliage to fruit.