Since March 1987, 304 evaluable patients with stage C and D prostate cancer have been entered into a prospective trial comparing Zoladex and Zoladex plus flutamide. To date, there has been no significant difference in over-all and progression-free survival between the 2 treatment groups. However, combined treatment produced a higher response rate (particularly in stage D patients) and a more rapid normalization of abnormal prostatic acid phosphatase levels. In addition, more prompt relief of bone pain was evident in the Zoladex plus flutamide group. However, significantly more side-effects were associated with combined treatment. These findings should be considered with caution because they form an interim analysis, and follow-up time is short. The results do suggest, however, that there is no particular advantage in using a combination of Zoladex plus flutamide compared to adding flutamide on failure of treatment with Zoladex alone.