Greer Garson (Mme. Marie Curie)
Walter Pidgeon (Pierre Curie)
Robert Walker (David LeGros)
Van Johnson (Reporter)
Albert Basserman (Prof. Jean Perot)
Margaret O'Brien (Irene at Age Five)
Henry Travers (Eugene Curie)
Eustace Wyatt (Doctor)
Ruth Cherrington (Swedish Queen)
Frederic Worlock (Businessman)
Michael Visaroff (Proud Papa)
Charles Trowbridge (Board Member)
Ray Teal (Driver)
Wyndham Standing (King Oscar)
Ray Collins (Lecturer)
James Hilton (Narrator)
Mariska Aldrich (Tall Woman)
Harold de Becker (Actor/Actress)
Tony Carson (Actor/Actress)
Nestor Eristoff (Board Member)
Nita Pike (People at Accident)
George Davis (Actor/Actress)
Howard Freeman (Prof. Constant)
Marek Windheim (Jewelry Salesman)
Arthur Shields (Businessman)
James Kirkwood (Actor/Actress)
Teddy Infur (Son)
Lumsden Hare (Prof. Roget)
Lisa Golm (Lucille)
Dorothy Gilmore (Nurse)
Victor Francen (President of University)
Edward Fielding (Actor/Actress)
Al Ferguson (Actor/Actress)
William Edmunds (Cart Driver)
Guy D'Ennery (Professor)
Gene Lockhart (Actor/Actress)
Miles Mander (Businessman)
Almira Sessions (Mme. Michaud)
Francis Pierlot (M. Michaud)
Gigi Perreau (Eva at Age 18 Months)
Isabelle Lamore (Actor/Actress)
Moroni Olsen (President of Businessmen's Board)
Alan Napier (Dr. Bladh)
Leo Mostovoy (Photographer)
George Meader (Singing Professor)
Reginald Owen (Dr. Becquerel)
C. Aubrey Smith (Lord Kelvin)
Dame May Whitty (Mme. Eugene Curie)
Elsa Basserman (Madame Perot)