The writer explains how the activities of Irish labor leader Jim Larkin in the United States attracted the attention of a young J. Edgar Hoover, then a functionary in the Aliens Registration office. Larkin was viewed as an undesirable presence in the United States due to his conspicuous labor activism. The interest of Hoover, future head of the FBI, in the investigation of Larkin is particularly revealing, in that it demonstrates, among other things, Hoover's increasing distrust of alien radicals and frustration at the rise of unionization in the United States. Moreover, the FBI file on Larkin reveals that neither the Attorney General's Office nor the FBI took action to thwart a plot to assassinate the labor leader. If Hoover's campaign to have Larkin deported had failed, Larkin's activism might have placed his life in danger.