['To investigate the relation between the incidence of radiation-induced tissue abnormalities in fetal brain and the extent of p53-dependent apoptosis.', 'Pregnant mice with wild-type p53(+/+), heterozygous p53(+/-) and homozygous mutant p53(-/-) fetuses received whole-body X-irradiation on day 13 of gestation. The extent of apoptosis 6 hr after irradiation and the incidence of tissue abnormalities 3 days after irradiation in the brain were evaluated by histological examination of brain mantle.', 'The percentage of apoptotic cells increased linearly with dose in p53(+/+) and p53(+/-) fetuses, but no increase was found in p53(-/-). Approximately twice the dose was necessary in p53(+/-) fetuses to induce an apoptotic response to the extent observed in p53(+/+). Fetuses with brain-tissue abnormalities, such as a destroyed ventricular lining and rosettes with a central hollow appeared at a dose of 1.5 and 3.0 Gy, and the incidence was markedly increased following a dose of 2.25 and 3.75Gy in p53(+/+) and p53(+/-) mice, respectively, but no fetus with tissue abnormalities appeared in p53(-/-) at up to 3.75 Gy. Approximately twice the dose was necessary in p53(+/-) fetuses to induce brain-tissue abnormalities to the extent seen in p53(+/+) mice.'] Are radiation-induced tissue abnormalities in fetal brain related to apoptosis immediately after irradiation?