Dragnet to The Bob Cummings Show

The main characters from Adam-12 appear as witnesses in an episode of Dragnet

Emergency! had a crossover with Adam-12 to find a boy who ran away from the hospital.

Both feature the fictional Trans Global Airlines

Diagnosis Murder's Dr Mark Sloan was defended by Matlock when Sloan was accused of murder

Mannix returned to TV on an episode of Diagnosis Murder to solve an old unsolved case with the help of Dr Mark Sloan.

Here's Lucy's Lucy Carter and Mannix's Mannix are held hostage in an episode of Here's Lucy.

Here's Lucy's Lucy Carter was visited in two episodes by The Bob Cummings Show's Bob Collins.