Felix and Murray played together in a band that specialized in 1930s music which was called "The Sophisticatos". In one episode, the band played country and western music and went by the name "Red River Unger and his Saddle Sores".
ABC worried that viewers would assume that Felix and Oscar were homosexuals because they lived together. As a prank, Randall and Klugman would often improvise scenes with homoerotic dialogue and send them to the network. A few of these can be seen in The Odd Couple Out-Takes (2005).
In the opening credits for the entire series, the type of luggage Felix is carrying changes.
When he is indoors (leaving his apartment or arriving at Oscar's) he is carrying a white suitcase. But when he is walking outside he is not carrying the white suitcase.