[en] Clinical records of 117 Segment III beagles sacrificed at 5 or 8 years of age were reviewed for evidence of testicular atrophy. Twenty-one percent of the 5-year-old dogs and 36 percent of the 8-year-old dogs had testicular atrophy confirmed by microscopic examination of the testicle sections. Atrophy was recognized in most dogs between 2 and 4 years of age, and at first recognition most were sterile. Twenty-one of the 5- and 8-year-old beagles had testicular tumors. The majority of the tumors were interstitial cell adenomas. No consistent association between radiation exposure, pedigree, or other diseases, such as hypothyroidism, and the development of testicular atrophy, infertility or neoplasms was found