A study of the flavonoid composition of the fruit of tangelo Nova by high-performance liquid chromatography and nuclear magnetic resonance revealed the presence of hesperidin, as the major flavanone, together with hesperetin 7-O-glucoside and prunin. The maximum levels of these flavanones are associated with the logarithmic phase of fruit growth. Treatment of recently set fruit with 20 ppm of benzylaminopurine delayed the fall of hesperidin concentration and accelerated this process in hesperetin 7-O-glucoside and prunin, compared with the evolution of these compounds in control fruit. The possible effect of benzylaminopurine on the biosynthetic pathway of these flavanones and/or on their transport in this plant material is discussed.