This marks the third Sherlock Holmes' movie starring Basil Rathbone where Holmes faces Prof. James Moriarty, after The Adventures of Sherlock Holmes (1939) and Sherlock Holmes and the Secret Weapon (1942). Curiously, Moriarty is portrayed by a different actor in each movie: George Zucco, Lionel Atwill, and Henry Daniell, respectively.
Although he is not seen, the only reference to Mycroft Holmes in the Basil Rathbone / Nigel Bruce series is made in this film.
Henry Daniell (Prof. Moriarty) had an earlier villainous role as William Easter in Sherlock Holmes in Washington (1943) and, as an ally of Holmes, Anthony Lloyd in Sherlock Holmes and the Voice of Terror (1942).
Only with the color version would the viewer know Lydia's final outfit was green; there is no mention of the wardrobe color in the movie. It was assumed in the original B&W version Lydia was wearing green sometime during the movie.
This was the first film in Universal's Sherlock Holmes series in which the main credit for Basil Rathbone and Nigel Bruce did not list the characters they played. All previous films contained "as Sherlock Holmes" and "as Doctor Watson" with their main credit.