Our results show a marked acute hematotoxicity of oral benzo(a)pyrene (BaP) in D2 mice as well as the extreme resistance of BDFl individuals to bone marrow toxicity induced by oral BaP. Continued oral BaP produced severe bone marrow depression in D2 mice affecting all myelopoietic lineages, but produced only moderate bone marrow depression in BDFl mice affecting erythropoiesis only. Pluripotent hematopoietic stem cells were almost completely destroyed in D2 individuals, but only reduced to approximately 40% in BDFl individuals after 7 days of BaP. D2 mice were killed by 13 days of continued oral BaP, but BDFl mice were still alive and in good condition even after 19 days of continued oral BaP. Analysis of the bone marrow and peripheral blood changes showed that severe toxic chemical bone marrow depression in D2 mice by continued oral BaP cannot serve as an experimental model system of acute aplastic anemia.