The number of animals surviving at 3 months post-BMT/total number of animals transplanted is shown. The percentage of surviving animals for each group is indicated in parentheses. A total of 155 newborn animals were transplanted. All of these animals in the 0, 200, or 400 cGy groups were 1 day old. Among the 800 cGy group, the first 25 newborn animals transplanted also were 1 day old. These animals all died within 1 week of the transplant. An additional 30 newborn 4-day-old animals were therefore transplanted in the 800 cGy group and 27 of these animals survived (2 ASMKO, 25 normal). Chi-square analysis showed that: (1) overall survival is significantly reduced at 400 and 800 cGy doses as compared with the 0 and 200 cGy groups (P < .0001); (2) that ASMKO mice have greater mortality than normal animals (P = .0001); and (3) that newborns have reduced survival as compared with adults (P = .017).