Medical countermeasures, including new drugs and vaccines, are necessary to protect the public's health from novel diseases and terrorist threats. Experience with the 2001 anthrax attack and the 2009 H1N1 pandemic suggest that there is limited willingness to accept such drugs and that minority groups may respond differently from others. We conducted 148 intercept interviews in the metropolitan Washington, DC, area, examining 2 hypothetical scenarios: a new respiratory virus and public exposure to high levels of radiation. Findings provide insights into key factors that affect whether diverse members of the public comply with recommended protective actions like taking emergency authorized vaccines. These insights can help improve how public health practitioners communicate during uncertain times.