Diagnosis: Murder to Lou Grant

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!

The Mary Tyler Moore Show's Georgette Baxter crossed over onto Hi Honey, I'm Home!

Lou Grant spun off of The Mary Tyler Moore Show