James Whitmore as Sgt. Ben Peterson

James Arness as FBI Agent Robert Graham

Joan Weldon as Dr. Pat Medford

Edmund Gwenn as Dr. Harold Medford

Onslow Stevens as Brig. Gen. Robert O'Brien

Sean McClory as Maj. Kibbee

Sandy Descher as The Ellinson Girl

Chris Drake as Trooper Ed Blackburn

Don Shelton as Trooper Capt. Fred Edwards

Fess Parker as Alan Crotty

Mary Alan Hokanson as Mrs. Lodge

Olin Howland as Jensen

William Schallert as Ambulance Attendant

Ann Doran as Child Psychiatrist

Dub Taylor as Railroad Yard Watchman

Leonard Nimoy as Army Sergeant

Richard Deacon as Bald Reporter at L.A. News Conference

Forbes Murray as Government Official

Kenner G. Kemp as Trooper #2

Charles Perry as Soldier

Dorothy Green as Matron

Willis Bouchey as Official at D.C. Meeting

Mary Lou Holloway as Blonde at Police Station

Dick York as Teenager in Police Station