Interest in the application of gonadotropin-releasing hormone (GnRH) analogues has grown dramatically since GnRH was first isolated in 1971, and the GnRH agonists have now firmly established themselves in the treatment of a variety of cancers, endometriosis, and fertility disorders. The first GnRH antagonists, cetrorelix and ganirelix, are about to reach the market for the first time. A number of the sessions at the 5th International Symposium on GnRH analogues in Cancer and Human Reproduction [Geneva, Switzerland; February 1999] dealt with the latest results on these antagonists, particularly cetrorelix and its therapeutic indications.