"Lux Radio Theater" broadcast a 60 minute radio adaptation of the movie onJune 11, 1945 with Dick Powell and Claire Trevor reprising their film roles.
Nat Pendleton is in studio records/casting call lists as a cast member, but did not appear in the film.
Audiences initially stayed away, thinking that "Farewell My Lovely", its original title, was yet another Dick Powell musical. When the studio changed the title to "Murder My Sweet", box office receipts picked up considerably.
Lindsay Marriott's car (driven to the jewelry rendezvous by Marlowe) is an Isotta Franchini 8A Spinto variant. This expensive Italian make was typically sold as a chassis with the owner selecting a custom body by a selected coach builder. The car used here is highly unusual (a 4-place convertible, split windshield, the original right hand drive was retained and features parade doors). Although the year is unknown it is likely a 1932. It featured a straight 8-cylinder engine and 4-wheel brakes.
Philip Marlowe's gun is a Colt Model 1903 Pocket Hammerless .32 semi-automatic, carried in what looks like a George Lawrence Co. shoulder holster.
RKO was on the verge of bankruptcy when it signed up aging matinée idol Dick Powell to make a series of musicals. Powell only signed under the proviso that he could play a straight dramatic role first, so he was cast as Philip Marlowe. Attached director Edward Dmytryk was initially horrified at this casting decision.