The efficacy of Casodex (ICI 176,334; Zeneca Pharmaceuticals, Macclesfield, UK), a nonsteroidal antiandrogen, in the treatment of advanced prostate cancer has been compared in two trials with castration, either surgical (bilateral orchitectomy) or medical, with the gonadotropin-releasing hormone agonist Zoladex (goserelin acetate; Zeneca Pharmaceuticals). The half-life of Casodex is 7 to 10 days, and allows once-daily dosing. The first trial was a prospective, randomized study involving 150 patients receiving Casodex, 50 mg once daily p.o., and 154 patients undergoing castration. There were no significant differences between the two groups in subjective responses, time to treatment failure, or time to objective evidence of disease progression. The other study involved higher doses, the dose being selected after patients had received one of two doses of Casodex, 100 mg/day or 150 mg/day, in a double-blind study. On statistical analysis, it was clear that the higher dose was more effective, and thus most patients taking 100 mg/day were switched to 150 mg/day. Again, Casodex treatment was compared with medical or surgical castration. The higher dose of Casodex is well tolerated with a similar adverse event profile as the lower dose of 50 mg/day. Follow-up is as yet too short for an analysis of efficacy.