• 
  Sam Waterston

  Robert Oppenheimer (7 episodes, 1980)
• 
  David Suchet

  Edward Teller (6 episodes, 1980)
• 
  James Waterston

  Peter Oppenheimer (1 episode, 1980)
• 
  Shane Rimmer

  Ed Condon (1 episode, 1980)
• 
  Ed Devereaux

  General Wilhelm Styer (1 episode, 1980)
• 
  Alexander Davion

  Arthur Compton (1 episode, 1980)
• 
  James Smith

  Dr. Harrison (1 episode, 1980)
• 
  Jay Benedict

  S.E.D. (1 episode, 1980)

• 
  Ed Bishop

  General Tom Farrell (1 episode, 1980)
• 
  Garrick Hagon

  Frank Oppenheimer (4 episodes, 1980)
• 
  Christopher Malcolm

  Steve Nelson (2 episodes, 1980)
• 
  Dave Hill

  James Tuck (1 episode, 1980)
• 
  Edward Hardwicke

  Enrico Fermi (6 episodes, 1980)
• 
  Barry Dennen

  Isidor Rabi (4 episodes, 1980)
• 
  Ray Charleson

  William Borden (1 episode, 1980)

• 
  Peter Banks

  Joseph Volpe (2 episodes, 1980)
• 
  Matthew Guinness

  Hans Bethe (5 episodes, 1980)
• 
  Sarah Brackett

  Priscilla Duffield (2 episodes, 1980)
• 
  Alexander Knox

  Henry Stimson (1 episode, 1980)
• 
  Phil Brown

  Lewis Strauss (2 episodes, 1980)
• 
  Kate Harper

  Jean Tatlock (3 episodes, 1980)
• 
  Pat Starr

  Alice Smith (1 episode, 1980)
• 
  Jana Shelden

  Kitty Oppenheimer  (6 episodes, 1980)
• 
  Manning Redwood

  General Leslie Groves (5 episodes, 1980)
• 
  Billy J. Mitchell

  Captain 'Deke' Parsons (2 episodes, 1980)
• 
  David Baxt

  Colonel John Lansdale (2 episodes, 1980)
• 
  Ron Berglas

  John Manley (3 episodes, 1980)
• 
  Jeff Harding

  M.P. (1 episode, 1980)
• 
  William Hootkins

  F.B.I. Agent (2 episodes, 1980)
• 
  Ryan Michael

  Student (1 episode, 1980)
• 
  Ralph Morse

  British Scientist (unknown episodes)