Androstenetriol (AET) and Androstenediol (AED) upregulate host immunity, leading to increased resistance against infections. AET augments IL-2, IL-3, IFN gamma levels, and counteracts hydrocortisone immune suppression. AET and AED at a dose of 0.75 mg/- and 8.0 mg/25-g mouse, protected 60 and 70%, respectively, of C57/BL/6J mice irradiated with a lethal dose. These hormones also protected mice irradiated with 6 Gy and infected with a coxsackievirus B4 LD50. AET significantly increased spleen lymphocyte numbers at 7, 14, and 21 days after a 6-Gy exposure. Fluorescent activated cell-sorter analysis of irradiated mice, spleen, and bone marrow showed that AET significantly augmented the myeloid precursor markers, CD11b/Mac-1, and B220 (pan B), as well as the absolute numbers of CD4+/CD8+ cells over the 21 days of testing. Overall, the data are consistent with AET/AED inducing a more rapid recovery of all hematopoietic precursors from the small number of surviving stem cells.