As part of a study of the role of the aryl hydrocarbon receptor (Ahr) in maintenance and senescence of hematopoietic stem cells (HSC), global gene expression profiling was done with HSC isolated from bone marrow restricted conditional Ahr-knockout and AhR floxed mice. HSC from young-adult (8 wk old) cAhR-KO mice had changes in expression of many genes related to HSC maintenance, consistent with the phenotype observed in Ahr-KO mice. Aged cAhR-KO mice (18 months old) also displayed alterations in peripheral white blood cell counts, serial repopulation potential and levels of ROS in bone marrow cells, consistent with previous observations on the role of AhR in the hematopoietic system. 22 samples: 5 young Ahr knockout, 6 old Ahr knockout, 5 young floxed Ahr, 6 old floxed Ahr