Digital rectal examination and transrectal ultrasound was used to evaluate the clinical status of 125 men previously treated for prostate carcinoma by definitive radiation. Transrectal ultrasound-guided biopsy of a hypoechoic lesion was performed on all 125 men, with 71.2% of them found to have persistent carcinoma. These irradiated carcinomas exhibited increased tumor aggressiveness by both histologic (Gleason score) and biologic (DNA ploidy) parameters. Following radiation therapy 30.6% of pretreatment diploid tumors were found to be aneuploid after treatment. Similarly, there was a 24% increase in the number of poorly differentiated (Gleason score 8 to 10) tumors following radiation therapy. A number of patients with persistent carcinoma postradiation therapy, but with clinically localized disease, may be "cured" by subsequent surgery. Salvage radical prostatectomy found localized cancer in 16 of 20 patients (80%). The use of transrectal ultrasound for early detection and staging was crucial for patient selection for definitive salvage therapy.