All four main cast members go by their real first name.
According to Patrick J. White in his book, The Complete Mission Impossible Dossier, 21 Beacon Street was Bruce Geller's inspiration for Mission:Impossible. In fact, in 1968, Filmways Productions, which owned the rights to 21 Beacon Street, sued CBS for copyright infringement.
"21 Beacon Street" was the address of Dennis Chase's office.
Although credited throughout, James Maloney appears in only 7 of the 13 episodes.
Sponsored by Kent cigarettes.