The events of September 11, 2001 and their aftermath increased awareness of the need to develop medical countermeasures (MCMs) to treat potential health consequences of a radiation accident or deliberate attack. The medical effects of lethal exposures to ionizing radiation have been well described and affect multiple organ systems. To date, much of the research to develop treatments for mitigation of radiation-induced hematopoietic damage has focused on amelioration of radiation-induced neutropenia, which has long been considered to be the primary factor in determining survival after an unintentional radiation exposure. Consistent with historical data, recent studies have highlighted the role that radiation-induced thrombocytopenia plays in radiation mortality, yet development of MCMs to mitigate radiation damage to the megakaryocyte lineage has lagged behind anti-neutropenia approaches. To address this gap and to foster research in the area of platelet regeneration after radiation exposure, the National Institute of Allergy and Infectious Diseases (NIAID) sponsored a workshop on March 22–23, 2010 to encourage collaborations between NIAID program awardees and companies developing pro-platelet approaches. NIAID also organized an informal, open discussion between academic investigators, product development contractors, and representatives from the U.S. Food and Drug Administration (FDA) and other relevant government agencies about drug development toward FDA licensure of products for an acute radiation syndrome indication. Specific emphasis was placed on the challenges of product licensure for radiation/nuclear MCMs using current FDA regulations (21 CFR Parts 314 and 601) and on the importance of animal efficacy model development, design of pivotal protocols, and standardization of irradiation and animal supportive care.