 Roddy McDowallCornelius | Cornelius |
 Kim HunterDr. Zira | Dr. Zira |
 Bradford DillmanDr. Lewis Dixon | Dr. Lewis Dixon |
 Natalie TrundyDr. Stephanie 'Stevie' Branton | Dr. Stephanie 'Stevie' Branton |
 Eric BraedenDr. Otto Hasslein | Dr. Otto Hasslein |
 William WindomThe President | The President |
 Sal MineoDr. Milo | Dr. Milo |
 Albert SalmiE-1 | E-1 |
 Jason EversE-2 | E-2 |
 John RandolphCommittee Chairman | Committee Chairman |
 Harry LauterGeneral Winthrop | General Winthrop |
 M. Emmet WalshAide | Aide |
 Roy GlennLawyer (as Roy E. Glenn Sr.) | Lawyer (as Roy E. Glenn Sr.) |
 Peter ForsterCardinal | Cardinal |
 Norman BurtonArmy Officer | Army Officer |
 William WoodsonNaval Officer | Naval Officer |
 Tom LowellOrderly | Orderly |
| GGene WhittingtonMarine Captain | Marine Captain |
 Donald ElsonCurator | Curator |
| BBill BondsTV Newscaster | TV Newscaster |
 Army ArcherdReferee | Referee |
 James BaconGeneral Faulkner | General Faulkner |
 Ricardo MontalbanArmando | Armando |
 John AldermanMarine Corporal (uncredited) | Marine Corporal (uncredited) |
 Alan BaxterGeneral (uncredited) | General (uncredited) |
 Jack BerleSecretary of State (uncredited) | Secretary of State (uncredited) |
| PPaul BradleyOfficial at Briefing (uncredited) | Official at Briefing (uncredited) |
| KKarl BruckGerman Newscaster (uncredited) | German Newscaster (uncredited) |
 Sam Chew Jr.Undetermined (uncredited) | Undetermined (uncredited) |
| RRobert ColeReporter (uncredited) | Reporter (uncredited) |
