Growing recognition that the modern pistol has several advantages over the revolver and the increasing use of semiautomatic and fully automatic weapons by criminals produced concerns about the adequacy of the current arms. In 1987, the Firearms Training Unit at the FBI Academy in Quantico, Va. initiated an effort to identify the best possible handgun for FBI agents. The analysis focused on bullet caliber, penetration, and wound size and used a series of tests to assess different types of ammunition. The initial tests used standard test barrels rather than specific weapons. The 10mm round produced the best results and was approved for the new pistols. The tests that led to this decision are available to other law enforcement agencies. In addition, the FBI will continue to test other calibers and bullets for law enforcement use. Photographs and table.