Jeanette MacDonald's older sister, Blossom Rock, signed with MGM and was given the name Marie Blake. Jeanette's character in San Francisco was named Mary Blake. Her sister used the name Blossom Rock when she played Grandma Addams on The Addams Family (1964).
Spencer Tracy, playing a priest, makes a note to himself in one scene, "That Rooney kid skipped Mass again..." Two years later, he again plays a priest in Boys Town (1938) and is charged with reforming a boy played by Mickey Rooney.
The comment that Spencer Tracy makes about the "Rooney kid" is an ad-lib (watch Jeanette MacDonald's expression reacting to it). Tracy had worked with Mickey Rooney earlier that year in Riffraff (1936) and knew that director W.S. Van Dyke abhorred retakes, priding himself on bringing in productions fast and under budget - hence his nickname, "One-Take Woody".
Al Shean (born Adolph Schoenberg), who plays the Professor in the film was once half of one of the most popular teams in vaudeville - Gallagher and Shean. He was also the younger brother of Minnie Marx, the matriarch of The Marx Brothers clan, and was instrumental in writing many of the first sketches that his madcap nephews first performed on the vaudeville circuit before their enormous success on Broadway and in Hollywood.
The character of Blackie Norton was inspired by a fellow writer of Robert Hopkins and Anita Loos, Wilson Mizner, who had worked on Broadway and at Warner Brothers and had died several years earlier, He was a notorious huckster,con artist, and womanizer, with connections in gambling and underworld circles.