[en] Studies on the metabolism, dosimetry, and effects of intravenously administered ¹³⁷CsCl in the Beagle dog are being conducted to aid in assessing the biologic consequences of exposure to ¹³⁷Cs such as might occur in the event of certain nuclear accidents. Effects of the chronic, relatively uniform whole-body exposure produced by ¹³⁷Cs are being compared with other diverse radiation dose patterns resulting from inhalation of radioactive aerosols. Sixty-six dogs were entered into the study; 6 with a mean initial ¹³⁷Cs body burden of 3780 μCi/kg, and 5 groups of 12 dogs each with mean initial ¹³⁷Cs body burdens of 2820, 1940, 1420, 970, and 0 μCi/kg. All six of the highest level dogs died 19 to 33 days post-injection with cumulative whole-body doses of 950 to 1400 rads. Three dogs in the 2820 μCi/kg level died at 24 to 27 days post-injection with cumulative whole-body doses of 860 to 910 rads. One dog in the 2820 μCi/kg level and one dog in the 1940 μCi/kg level died at 77 and 81 days after injection with cumulative whole-body doses of 1300 to 1400 rads. These early deaths were attributed to severe bone marrow damage which was reflected in an early dose related pancytopenia. A dog injected with 1900 μCi/¹³⁷Cs/kg died 693 days post-injection with necropsy findings attributed to shock. A dog injected with 2800 μCi/kg died 1594 days post-injection with aspiration pneumonia and a dog with 2900 μCi/kg was euthanized 1704 days post-injection with severe arthritis. A control dog died 647 days after initiation of the study with clinicopathological manifestations of auto-immune hemolytic anemia. Forty ¹³⁷Cs dogs and 11 controls are surviving at 2047 to 2301 days after being placed on experiment. The surviving ¹³⁷Cs dogs had initial body burdens that ranged from 880 to 3000 μCi/kg and received cumulative whole-body doses of 550 to 2200 rads. Serial observations are continuing on all survivors. (U.S.)