Chlorambucil plus prednisolone were administered to 11 patients with metastasis hormone refractory prostatic cancer, and the results were contrasted with a previously reported series of 23 similar patients treated with the chemical conjugate of these two agents, known as prednimustine or Leo 1031. The conjugated form of treatment (Leo 1031) had a limited therapeutic advantage, in that 3 patients experienced shrinkage of an enlarged prostate, 2 of whom also had elevated acid phosphatase levels return to normal and 5 others experienced only subjective improvement. There were, however, more adverse side effects in this group than those noted in patients treated with the combination of agents. Patients treated with the combination of drugs experienced no appreciable tumor shrinkage and none had acid phosphatase return to normal, although some reduction was noted in 8 of 11 patients who had elevated levels initially. Two of the 11 patients were considered stable for twelve months and one other remained ambulatory with mild pain for six months. Thus, to the degree that these studies permit, it is judged that the conjugated agent may have some limited therapeutic advantage not observed when the unconjugated agents were used.