Louis Calhern replaced Frank Morgan in the role of Buffalo Bill Cody after Morgan died of a sudden heart attack shortly after filming began. In Buffalo Bill's very first appearance on his horse, Frank Morgan is visible a split second before the shot of Calhern.
Judy Garland and Frank Morgan appeared together in The Wizard of Oz (1939), and were scheduled to appear in this film. Garland was fired because of health problems, Frank Morgan died shortly after filming began.
Betty Hutton and Howard Keel did not get along during filming. Keel thought that Hutton cared more about her career than her co-stars.
Writers Dorothy Fields and Herbert Fields and producers Richard Rodgers and Oscar Hammerstein II had originally arranged for Jerome Kern to write the musical score. After Kern died suddenly, he was replaced by Irving Berlin. This was the first time that Berlin wrote a score for a show with an existing plot. In his many musical plays and films, the songs were written first, then the scripts were written for the situations suggested by the songs.