CHEMICAL SPRAY THINNING has proved to be a promising way to reduce the costs and labor needed for thinning stone fruits. Dinitro materials like, Elgetol sprays and D.O.C. dusts have been used more than 25 years for thinning out heavy fruit sets in plums and peaches. To be most effective, dinitro materials must be applied during a one- to two-day period before full bloom (at 60 to 90 per cent of full bloom) when set is unknown and frost and rain are still crop hazards. The erratic quality of the thinning with dinitros plus the necessity for early season application has limited the use of these chemicals to extra heavy setting fruit varieties.