[en] Purpose: To determine the effect of external beam radiation therapy on serum prostate-specific antigen (PSA) production by the benign prostate. Methods and Materials: We studied a cohort of 24 men receiving treatment for cancer of the bladder or rectum. The radiation fields in all cases encompassed the prostate gland, and none of the patients were known to have prostate cancer. All patients had 2 or more PSA estimations obtained in the years following their radiation treatment. A second group of 46 patients who had undergone radical external beam radiation therapy for prostate cancer and who were clinically disease free 8-22 years later were also observed, with a median of 5.8 years of PSA observations. Results: Only 3 of the 24 patients in the first group showed a significant rise of > 0.2 ng/ml in their serum PSA levels, with a median of 3.3 years follow-up from the first PSA test. Seven of 24 showed progressive declines, and 14 of 24 showed steady levels. The median PSA for this group was ≤ 0.5 ng/ml. Only 6 of the 46 in the second group showed a PSA rise of > 0.2 ng/ml. Thirty-four had stable values, and 6 had further declines. Again, the median PSA for the entire group was ≤ 0.5 ng/ml. Conclusion: Recovery of prostatic secretory function is an uncommon event after external beam radiation. The concern that this might significantly confound new definitions of biochemical failure after radical radiation for prostate cancer that are based on progressively rising PSA values thus appears to be unfounded