There are two FDA-approved pharmacological countermeasures against external penetrating ionizing radiation for use outside the clinic: Neupogen® (G-CSF) and Neulasta® (pegylated G-CSF). Six radiation countermeasures for ARS have U.S. Food and Drug Administration (FDA) Investigational New Drug (IND) status, meaning they can be tested for safety in humans. These are 5-androstenediol (5-AED, Neumune), genistein (BIO300), Ex-Rad®, Entolimod (CBLB502), OrbeShield™, and HemaMax™ (rhIL-12). AFRRI has been involved in the development of five of these seven agents. 5-AED and genistein were conceived as countermeasures and initially developed at AFRRI. Ex-Rad® and CBLB502 were initiated at private companies; AFRRI collaborated at early stages. AFRRI performed some of the earliest work on cytokines and growth factors as radiation countermeasures. This led to inclusion of Neupogen® in the Strategic National Stockpile. AFRRI continues an intensive program on identification and development of radiation countermeasures to be used by military and civilian personnel. This work depends on studies aimed at understanding the mechanisms of radiation injury and countermeasure efficacy. AFRRI has been funded for initial development of countermeasure candidates. Advanced development is carried out by companies or other government agencies.