Ronald Colman
— Dr. Martin Arrowsmith
Helen Hayes
— Leora Tozer Arrowsmith
Richard Bennett
— Gustav Sondelius
A.E. Anson
— Professor Max Gottlieb
Clarence Brooks
— Dr. Oliver Marchand
Alec B. Francis
— Twyford
Claude King
— Dr. Tubbs
Bert Roach
— Bert Tozer
Myrna Loy
— Joyce Lanyon
Russell Hopton
— Terry Wickett
David Landau
— State Veterinarian
Lumsden Hare
— Sir Robert Fairland
Erville Alderson
— Pioneer (uncredited)
Ward Bond
— Cop (uncredited)
Beulah Bondi
— Mrs. Tozer (uncredited)
Florence Britton
— Miss Twyford (uncredited)
Nora Cecil
— Nurse (uncredited)
Sidney De Gray
— Dr. Hesselink (uncredited)
Cyril Delevanti
— Committee Member (uncredited)
Walter Downing
— City Clerk (uncredited)
Gibson Gowland
— Committee Member (uncredited)
Sherry Hall
— Reporter (uncredited)
Theresa Harris
— Native Mother (uncredited)
Raymond Hatton
— Drunk (uncredited)
Charlotte Henry
— Pioneer Girl (uncredited)
George Humbert
— Italian Uncle (uncredited)
DeWitt Jennings
— B.W. Tozer (uncredited)
Mike Lally
— Reporter (uncredited)
Lillian Lawrence
— West Indies Townswoman at Meeting (uncredited)
Carl M. Leviness
— Ship's Passenger (uncredited)