In a retrospective study, the extent of reactions of different types of prostatic carcinomas to external or interstitial radiotherapy was compared with reactions to hormonal therapy. It is shown that prostatic carcinomas of different grades of differentiation can be divided into two main subgroups with distinctly different survival rates; i.e., prostatic carcinomas grades of malignancy Ib/IIa and grades IIb/III. Within an observation time of 10 years, the prostatic carcinoma grade of malignancy Ib/IIa shows a good response to external and interstitial radiotherapy. None of the patients died of the prostatic carcinoma. In the more poorly differentiated prostatic carcinomas, 2 out of 11 patients with external radiotherapy died of the carcinoma. The death rates from disease after hormonal therapy were higher, and the survival times were very short without therapy. Regressive changes are much more distinctly expressed in the better-differentiated carcinoma group. Differential diagnostic difficulties between regressive changes in carcinomatous glands and normal glands could be resolved by immunohistochemical proof of high-molecular-mass cytokeratin in basal cells.