Promised Land to The Many Loves of Dobie Gillis

Promised Land's Russell Greene helped his boss Ryan Matthews face his families past, then Ryan crossed-over onto Diagnosis Murder to ID the body of one of his ex-wife's old friends

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 Mary Jane Lewis was originally a character on The Lucy Show (also called The Lucille Ball Show).

Mr. Mooney from The Lucy Show was on Hi Honey, I'm Home!

Many Loves of Dobie Gillis' title character crossed over onto Hi Honey, I'm Home!