In June of 2009, real-life F.B.I. Director Robert S. Mueller III honored Efrem Zimbalist, Jr. with a plaque and badge, making Zimbalist an honorary F.B.I. Agent for his work on the series.
For this series, Efrem Zimbalist, Jr. was provided with an F.B.I. identification card that had a recent photograph of him, fingerprints from his Army service, and an identification number that was only one digit less than a genuine number.
F.B.I. memos, which were recently released under the Freedom of Information Act, have revealed that the real F.B.I. had a veto over casting for guest stars on the series. According to the memos, Robert Blake and Bette Davis were barred from making guest appearances on the series.
Originally sponsored by the Ford Motor Company, which supplied all of the vehicles used on the show.
In the closing credits, Inspector Erskine (Efrem Zimbalist, Jr.) could always be seen driving off in the current year's Ford Mustang.
J. Edgar Hoover served as Series Consultant until his death in 1972. He never appeared in front of the camera.
Of the series that Quinn Martin produced, this series was his longest running of all. It aired nine seasons.