The segment of Password with Sondheim and Lee Remick was on this afternoon, and it was a lot of fun. Both Sondheim and Remick were very good at the game. There were multiple players in the episode, though, and he was only on for about 10 minutes.
The segment is from 1966. He was introduced as a creator of West Side Story, Gypsy, and Forum. (I don't remember the exact wording of his intro.) When asked about his next musical, he said he was working on "The Girls Upstairs."
Interestingly, at least four times in the episode, someone gave a clue to the first person, and the second cluegiver just gave the exact same clue on their turn! Unsurprisingly, that helped no one.