In burros exposed to 50 r or 25 r fractional daily total-body cobalt-60 gamma radiation the mean survival times were 30 and 63 days, respectively. Hematologic depression was observed in the 25 r daily dose group. Lymphocytes showed the greatest decrease. Eo-sinophils showed the least decrease. Platelets were significantly reduced at accumulated dose of 725 r. A pronounced hyperferremia which continued until near death was observed after 500 r in the 50 r/day animals and after 200 r in the 25 r/day group. The clinical syndrome was characterized by weight loss, ulcerations, hyperesthesia and a hemorrhagic syndrome. The response was similar to that previously reported in burros receiving 100 to 400 r/day.