1. Flowering clusters of Black Corinth and Thompson Seedless grapes at berry-shatter stage were dipped in GA1 or GA3 at various concentrations. Response to each compound was about equal, as judged by greater berry size in both varieties. 2. GA3 and KGA3 concentrations of 0, 5, 20, or 50 p.p.m. were separately applied to Thompson Seedless at shatter stage by dipping clusters or spraying vines. The compounds were about equally effective in inducing larger berries. 3. In dipping and/or spraying experiments, Black Corinth, Hunisa, and Ohanez showed no greater response to KGA3 and 4-CPA in combination than to either compound applied separately. 4. Carignane clusters at prebloom stage were dipped in KGA3 in the range 0-100 p.p.m. Pollen germinability was markedly decreased by KGA3 at 5-100 p.p.m. and was nil at 100 p.p.m. Treatment with KGA3 at 100 p.p.m. resulted in more berries with a single seed and fewer with three or four seeds. 5. Germinability of pollen obtained from Carignane clusters that had received no chemical treatment was markedly reduced by KGA3 solutions at 1-25 p.p.m., indicating that the compound can act as a pollenicide. 6. Emasculated flowers on girdled or ungirdled vines of Black Corinth, Thompson Seedless, and Tokay received applications of KGA3 and 4-CPA. Girdling resulted in fruit-set in emasculated flowers of Black Corinth, and a good set on ungirdled canes followed treatment with KGA3 or 4-CPA. Emasculated Thompson Seedless flowers failed to set fruit, whether the canes were girdled or ungirdled, but treatment with KGA3 or 4-CPA resulted in setting of fruit. In Tokay, a seeded variety, application of either KGA3 or 4-CPA enhanced the fruit-set from emasculated flowers on ungirdled vines.