A new longer-acting depot formulation containing 10.8 mg Zoladex administered every 12 weeks was compared to the 3.6-mg Zoladex depot administered every 28 days, in a randomised trial in patients with advanced prostatic carcinoma in which pharmacodynamic efficacy and safety were assessed. Effective induction of mean serum testosterone suppression into the surgically castrate range by 21 days and maintenance of suppression for the duration of therapy was achieved with both the 3.6-mg and the 10.8-mg depot formulations. The Zoladex 10.8-mg depot was well tolerated both locally and systemically. This new formulation which is equivalent to three successive 3.6-mg depots will provide a more convenient dosing regime for both patient and doctor in this indication.