Don TaylorDirector
Roddy McDowallCornelius
Kim HunterDr. Zira
Bradford DillmanDr. Lewis Dixon
Natalie TrundyDr. Stephanie Branton/Stevie
Eric BraedenDr. Otto Hasslein
William WindomThe President
Sal MineoDr. Milo
Albert SalmiE-1
Jason EversE-2
John RandolphChairman of the President's Committee of Inquiry
Harry LauterGeneral Winthrop
M. WalshGeneral Winthrop's Aide
Roy GlennLawyer
Peter ForsterCardinal
Norman BurtonArmy Officer
William WoodsonNaval Officer
Tom LowellOrderly
Gene WhittingtonMarine Captain
Donald ElsonCurator
Army ArcherdReferee
Bill BondsTV Newscaster
James BaconGeneral Faulkner
Ricardo MontalbanArmando
John AldermanMarine Corporal (uncredited)
Steve RobertsGeneral Brody (uncredited)