Dr. Seuss decided to bring together two of his most famous creations in a half-hour special for ABC that served as the official coda to DePatie-Freleng Enterprises. The Grinch Grinches The Cat in The Hat, first broadcast in May 1982, was finished by DFE successor Marvel Productions, just as they had completed the Dennis The Menace special, Mayday For Mother, a year earlier, as we discussed the other day.
Mason Adams (Lou Grant), who had been doing voiceovers for Smuckers jellies and jams around this time, narrates and voices the Cat. Bob Holt, a long time DFE standby, is the Grinch.
Holt became the 3rd actor to essay the voice of the Grinch after Boris Karloff (whom Holt is impersonating) and Hans Conreid. Adams was the 2nd to voice the Cat, following Allan Sherman.
The plot seems to be something akin to the usual Saturday morning fare of the day, and one wonders if Seuss had ever been approached about doing a Saturday morning show of some kind.