To determine the fate of gibberellic acid (GA(3)), solutions were incubated for 24 hours with or without barley endosperm and were subsequently applied to dwarf maize seedlings. Hormone activity appeared to increase as a result of incubation with endosperm. This apparent increase in GA(3) concentration was probably due to a synergistic interaction between GA(3) and endosperm constituents, particularly carbohydrate, released during the incubation period. It is concluded that relatively little hormone is inactivated during the initiation of endosperm mobilization.