Our purpose in this report is to present data on 75 cases of prostatic carcinoma treated by orchiectomy at the University Hospital and observed for periods of at least six months following that procedure. The diagnosis was confirmed by microscopic examination in 60 of the cases; in 15 there was no material removed for biopsy, the diagnosis being established on the basis of characteristic findings on rectal examination, with evidence of metastases by x-ray examination or by elevated serum phosphatase levels in all except three. Preoperative acid phosphatase determinations by the method of King and Armstrong were carried out in 28 of the cases. At the time this therapeutic project was begun, these determinations were not being made at the University Hospital Laboratory. Eleven cases (39 per cent) showed elevated serum acid phosphatase levels of 6 King-Armstrong units or higher. The preoperative determinations in these cases are given in the