Effects of various concentrations of Dormex (a.i. 49% hydrogen cyanamide) on fruit thinning of ‘Rome Beauty’ apple (Malus domestica Borkh.), ‘Friar’ and ‘Simka’ plums (Prunus salicina Lindley) were studied. A full bloom application of Dormex at all tested concentrations decreased ‘Rome Beauty’ apple fruit set and yield, and increased fruit weight. Dormex at 0.25% (v/v) resulted in adequate apple thinning, indicated by production of an optimum fruit weight (320 g). Prebloom and full bloom applications of Dormex at greater than 0.75% reduced plum fruit set and yield in ‘Friar’. Full bloom application of Dormex at 0.50% showed a satisfactory fruit set, yield, and fruit weight in ‘Friar’ plum. Prebloom Dormex application had no significant effect on `Simka' plum fruit set or yield, but full bloom application decreased fruit set and yield.