Interactions between the growth retardant daminozide (a substituted succinamic acid) and a subsequent application (1 or 10µg) of either gibberellin A 3 , A 9 or A . ., on stem extension in Chrysanthemum morifolium cv. Bright Golden Anne, indicated that pre-treatment of plants with daminozide largely prevented the response to GA,, as well as to GA 9 . The daminozide-GA3 interaction on total stem length was dependent upon the dose of GA 3 such that, by flowering time, 1 µg of GA 3 had virtually eliminated the retardant effect, while 10 µg of GA 3 increased stem length to a value similar to that achieved by control shoots receiving 10 µg of GA 3 . In contrast, prior application of 2, 2'dipyridyl (an inhibitor of hydroxylation in some plant and animal systems) had no significant influence on the time courses of response to any of the GAs . In the absence of daminozide (and 2, 2'-dipyridyl) all three GAs were very active in promoting internode extension soon after their application . If 2, 2'-dipyridyl can block hydroxylation reactions in chrysanthemum tissues, the results do not support the hypothesis that daminozide restricts GA 9 -( or GA, a -) induced stem elongation by preventing the hydroxylation of GA9 .