To determine the role of p53 in controlling the induction of PHLDA family genes in human and mouse hematopoietic cells following ionizing radiation, we first examined mRNA expression of PHLDA1, PHLDA2 and PHLDA3 in isogenic human MOLM13 acute myeloid leukemia cells that harbor wild type p53 (p53+/+), no p53 (p53−/−) or a p53R175H mutant protein (p53R175H/−) after exposure to 0 or 2.5 Gy X-rays. The gene discussed is PHLDA1; the disease is acute myeloid leukemia.