Estramustine phosphate, a nor nitrogen mustard derivative of estradiol 17-beta-phosphate, was introduced in the treatment of prostatic carcinoma in 1966. Until March 1975, 466 patients have been reported on this treatment in open clinical trials: 82% of the patients were in stage IV. In 402 patients, nonresponsive to previous estrogen therapy, signigicant improvement occurred in 55%. In 64 previously untreated patients there was a favourable response in 83%. Side-effects were mainly bone marrow suppression. liver disturbance, thrombophlebitis following intravenous injection, and gastrointestinal troubles, mainly following oral administration. A prospective, randomized study comparing oral estramustine phosphate and conventional estrogen therapy in carcinoma of the prostate is in progress.