We studied the effect of exogenous applications of GA$_3$ on rubisco activation in soybean leaves. Activity at 0.1 $mu$M GA$_3$was significantly greater than in leaves receiving no treatment. Rubisco content showed patterns of change similar to that for activity. These data suggest that activity was associated with the amount of rubisco protein, and that the activation and induction of rubisco was promoted by GA$_3$. The degree of intensity of the 50- and 14.5-kD polypeptides (identified as the large and small subunit, respectively of rubisco by SDS-PAGE analysis) at 0.1 $mu$M CA$_3$ was significantly higher than that for the control, indicating that GA$_3$ affected both subunits. The stimulation effects of rubisco activation by GA$_3$ seem to be caused by the expression of rubisco genes at the transcriptional level. Assuming that these GA$_3$ effects were related to rubisco activase, we also determined the activity and content of that enzyme. Its activity at 0.1 $mu$M GA$_3$ increased more than did the control, A similar pattern of change was observed for rubisco activase content. The intensity of two 46- and 42-kD polypeptide bands at GA$_3$ was higher than for the corresponding bands at the control. Therefore, the change in rubisco activase levels may lead to alloyed levels of rubisco.