Acidification of treatment solutions from pH 7 to 4, with either citrate-phosphate (CP) buffer or with dimethylglutaric acid–NaOH (DMG) buffer, increased [14C]GA3 uptake by ‘Marsh’ grapefruit (Citrus paradisi Macf.) peel. Acidification was effective also when wax was removed with organic solvents and under low and high relative humidity. The GA3-induced delay of coloration of ‘Minneola’ (Citrus paradisi × C. reticulata Blanco) tangelo and ‘Ortanique’ (C. sinensis × C. reticulata) was increased similarly by acidification with either buffer. Acidification with either buffer permitted the use of lower GA3 concentrations than those required to obtain the same physiological effect with neutral solutions. Acidification also delayed fruit senescence in field trials with ‘Clementine’ (Citrus reticulata Blanco) tangerines sprayed with 5 ppm GA3 + 0.1% H3PO4. Uptake of [14C]GA3 progressively increased by reducing pH from 7 to 3. With [3H]GA4, acidification improved the uptake only in the range of pH 8 to 5. This difference seems to be related to the more lipophilic nature of GA4.