The criteria for the diagnosis of progression of prostatic cancer after primary treatment by androgen suppression (oestrogen escape) were studied in 30 patients. Objective criteria are essential for this diagnosis and in this study the bone scan was the most useful criterion. Twenty-one of these patients had a secondary orchiectomy: one patient showed a partial objective response and 3 had a subjective response. It is concluded that an orchiectomy following failed primary oestrogen therapy is an ineffective procedure and therefore unjustifiable and that alternative treatments must continue to be evaluated.