A 6-month formulation of the gonadotropin-releasing hormone agonist triptorelin embonate (designed to deliver 22.5 mg of triptorelin over a 6-month period) has been developed for use in the treatment of advanced prostate cancer. Following intramuscular administration of the 6-month formulation of triptorelin embonate 22.5 mg to men with advanced prostate cancer (subset of 15 patients from the pivotal clinical trial), serum testosterone levels initially increased, followed by a rapid, sustained decrease. Castrate serum testosterone levels (i.e. < or =1.735 nmol/L) were achieved in a geometric mean time of 18.8 days. The 6-month formulation of triptorelin embonate achieved and maintained castrate serum testosterone levels in patients with advanced prostate cancer (n = 120), according to the results of the pivotal, noncomparative, multicentre trial (patients received intramuscular triptorelin embonate 22.5 mg on day 1 and at month 6 [week 24]). By day 29, 97.5% of patients had castrate serum testosterone levels. Castrate serum testosterone levels were maintained from months 2 to 12 in 93.0% of patients. Prior to the second injection at month 6, 98.3% of patients had castrate serum testosterone levels, and 98.3% of patients had castrate serum testosterone levels at study completion. The 6-month formulation of triptorelin embonate 22.5 mg was generally well tolerated in patients with advanced prostate cancer; adverse events were of mild severity in the majority of patients. Drug-related adverse events (e.g. hot flushes) were consistent with the pharmacological action of triptorelin. Injection-site reactions occurred in 6.7% of triptorelin embonate recipients.