the present trial was carried out aiming to increase fruit set of 'monte parnaso' (citrus sinensis [l.] osbeck) navel oranges budded on trifoliate orange (poncirus trifoliata [l.] raf.) rootstocks grown in the state of rio grande do sul, brazil. in 1996, six-year-old navel orange trees were sprayed with growth regulators combined or not with girdling. the following treatments (t) was conducted: t1) control; t2) spraying of five ppm of ga3 at the end of petal fall; t3) girdling 10 days after petal fall; t4) t2 plus t3; t5) spraying of 15ppm 2.4-d; t6) t4 plus t5; t7) girdling in november 15th; t8) t5 plus t7; t9) t6 plus t7; t10) t6 plus spraying of 10ppm of ga3 and 15ppm of 2.4-d in may of 1998; t11) t9 plus spraying of 10ppm of ga3 and 15ppm 2.4-d in may of 1998. the results showed increased the weight (45%) and number of fruits produced. the treatments did not affect the fruits average and total soluble solids, titratable total acidity and percentage of juice contents.