A morning blast at the Alfred P. Murrah Federal Building, Oklahoma City, OK, on April 19, 1995, killed 168 persons and injured more than 500 in the worst terrorist attack in U.S. history. Hospital workers, physicians, and volunteers at nine hospitals there mobilized, put their disaster emergency plans into operation, and treated 466 persons in emergency rooms--many of them later being admitted as patients. To complicate matters, two of the hospitals received bomb threats called in after the disaster. This report will look at the security plans put into force by each of the nine hospitals; the handling of the great influx of persons, including victims, relatives, friends, concerned persons, volunteers, and the news media; and the lessons hospital officials learned from their experiences.