Gibberellin A3 (GA) applied to virus-infected sour cherry (Prunus cerasus L., `Montmorency') trees inhibits flower initiation and promotes spur formation. However, response to a given dose may vary. Differential foliar absorption has been suggested as a major source of this variation. Therefore, we studied if surfactants would reduce variation in GA absorption. Uptake through the abaxial surface exceeded that through the adaxial surface by about one order of magnitude (adaxial surface 1.1 vs 7.8% in 1988, 0.7 vs 16.6% in 1989). GA uptake was markedly affected by surfactants. Over a 24-hr uptake period, Activator 90 and Ortho X-77 were most effective (abaxial surface 38.3 and 37.4% in 1989), whereas Regulaid did not affect GA uptake. L-77 significantly depressed absorption (abaxial surface 9.1% in 1989). In addition to the level of uptake, surfactants also changed GA absorption kinetics. Penetration increased linearly over a 96-hr time period when Regulaid was included. However, with Ortho X-77, uptake was rapid initially but levelled off within 96 hr. These findings will be discussed in relation to biological response data obtained in the field experiments.