The effects of 3-deoxygibberellin C (DGC) on the growth-promoting actions of gibberellins A(1), A(2), A(3), A(4), A(5), A(7), A(8), A(9), A(13), A(18), A(19), A(20), and A(23) (GAn) as well as 13-deoxygibberellin A(5) (deoxy-GA(5)) were tested with seedlings of gibberellin-deficient dwarf mutants (d(2) and d(5)) of maize (Zea mays L.). It was found that DGC promoted the actions of gibberellins having both C-1 double bond and C-3 axial hydroxyl group, and it inhibited the action of gibberellins having the saturated ring A and lacking the C-3 axial hydroxyl group, whereas it did not affect that of the ones having the hydroxyl group. The presence of C-2 double bond, as in GA(5) and deoxy-GA(5), diminished the inhibitory action of DGC. The DGC inhibition was alleviated by raising the doses of the relevant GAs, suggesting that it is a competitive inhibition. These results and the finding that the growth of normal maize and rice seedlings are inhibited by DGC indicate that GA(9), GA(19), GA(20) or other gibberellins having ring A of the same structure are involved in the growth of these plants as active form(s) or as intermediate(s) leading to the active form(s).