William Conrad appeared on many early episodes of the show as Frank Cannon. Barnaby and Betty had originally appeared on Cannon (1971) after Barnaby's son Hal, who was a good friend of Frank's, was murdered. Cannon helped Barnaby eventually track down his son's killers.
After production of "Barnaby Jones" completed, producers were considering a TV-movie crossover between this show and Buddy Ebsen's previous show The Beverly Hillbillies (1962). The storyline would open with Millionaire Jed Clampett (played by Ebsen) being kidnapped, and Barnaby Jones (also played by Ebsen) hired to locate him. That ATV-movie was never produced, although a similar storyline was created for the 1993 big screen version of "Hillbillies", with Ebsen returning in a cameo as Barnaby Jones, hired by Miss Hathaway to find the missing Granny.