Testosterone propionate (Neo-Hombreol), 25 mg. intramusc. every other day, was used in the treatment of 3 patients with mammary cancer. In the first patient there was a surprising improvement, almost reaching a clinical cure. In the 2d patient, some improvement occurred even though androgen therapy was started at a very advanced stage when there were numerous metastases and extreme cachexia. The 3d patient had an ulcerated tumor of the breast and, although the observation period for this case is very short, the secretion of the ulcer was noticeably decreased and the granulations, which were sloughing before, exhibited a reddish, clean aspect after a period of testosterone therapy.