Glenn Ford was at a lull in his career when he was offered the part of Dr. King. Even so he made it a condition that he receive top billing--which rightfully belonged to the film's' star Eleanor Parker--or he wouldn't do the part. Parker said she always cared more about the projects than the billing, but this is one time she regretted giving in because she very much wanted the credit as star of the picture. She also says that Ford shamelessly tried to upstage her at every chance by walking away from her, and the camera, forcing her to turn her back to the camera to interact with him.
Eleanor Parker can read music and has perfect pitch as a singer. She decided to study the scores of the opera songs used in this film on her own. She rented a cabin in Lake Arrowhead, California, and played the records while singing along until she had the breathing and phrasing memorized. Then when filming the scenes, instead of lip-synching to the tracks recorded by Eileen Farrell for the movie, she sang full voice (but an octave lower). She is proud of the fact that they never had to do a re-take in order to "match" the tapes--she nailed it on the first take every time.
Greer Garson was originally set to play the lead role of Marjorie Lawrence, but the film was postponed for about one year. Garson wanted the part very badly and researched the role extensively. One month after she left MGM (the studio filming the movie), Eleanor Parker was cast.