Eucalyptusnitens(Dean & Maiden) Maiden grafts growing as espaliers at Ridgley, Tasmania, and Canberra, Australian Capital Territory, were treated with paclobutrazol as a single collar drench application. Umbel production was enhanced for 3 years at Ridgley and 2 years at Canberra. Canberra grafts were also treated by trunk injection, which proved effective only in the 1st year. Untreated grafts did not produce an appreciable number of umbels until year 3. Paclobutrazol reduced the level of endogenous gibberellins. Close association between gibberellin levels and increases in reproductive activity ofE.nitensgrafts suggests that the effects of paclobutrazol treatment may be mediated via a reduction in the rate of gibberellin biosynthesis.