This movie was to begin production in 1942, but Myrna Loy refused the part. Instead, she went to New York where she married car rental heir John Hertz Jr. and worked for the Red Cross war-relief effort. The movie almost began shooting with actress Irene Dunne as Nora Charles.
Liberal drinking of alcohol, a mainstay of the first four "Thin Man" movies, was curtailed for this movie due to wartime liquor rationing.
Replaced for this movie was the canine actor who had played Asta since the first Thin Man film. The original dog, Skippy, outgrew the part.
Nick is lying in a hammock 22 minutes into the movie, with a copy of "Nick Carter, Detective" magazine. This issue is Volume 7, #3 (May 1936), thus making it 8 years old at the time of filming. The use of this magazine is an homage to the long-time pulp detective Nick Carter, from whom Nick Charles got his own first name and surname initial.
In the sequence where the rumor is going around town that Nick is on a case, the woman at the butcher shop is prominently holding a war rationing stamp book in her right hand--something that would have been very familiar to audiences at the time. Meat rationing began in March 1943 and didn't end until November 1945. Additional evidence of wartime rationing is the poster at the train station showing the smiling GI holding his canteen cup that reads, "Do with less--so they'll have enough". (Office of War Information poster #43, 1943)