Earlier work has shown that gibberellin treatment of individual flowers or small fruits of many citrus varieties gave increased fruit set. The Washington Navel orange was selected for field scale experiments, entire trees being sprayed to determine the effect on fruit set. Phytotoxic responses of twig dieback and leaf drop resulted. Fruit set was not increased by overall gibberellin sprays. Often a significant reduction in yield resulted. Fruit size and quality responses are related to gibberellin concentration and date of application. The difference between response to applications on individual flowers or fruits and response to spraying the entire tree suggests the possible involvement of water relations and also indicates an influence of the gradient flow of gibberellin between the fruit and branch. Certain similar and contrasting responses of citrus to gibberellin sprays and some other plant growth regulators are noted.