Four major cling peach varieties (Halford, Peak, Paloro, Carolyn) were effectively thinned with 3-CPA. Proper timing based on ovule length (8.5 to 9.5 mm is best) was essential for best thinning. The best sprays were of 300 ppm applied at 400 gallons per acre, or 1.6 gallons of formulated material per acre. Slight phytotoxicity usually occurred whenever thinning was obtained but was limited to a few yellow leaves which dropped two weeks later and some leaf tipburning and twisting. Fruit harvested after 3-CPA sprays appeared equal in size, maturity and quality to hand-thinned fruit. A small amount of pole or touch-up hand thinning was usually needed in addition to the thinning sprays to attain good commercial thinning.