Toonfomercial: The Flintstones learn about cancer (1966)

 After The Flintstones ended its primetime run in 1966, Hanna-Barbera was commissioned to produce a PSA for the American Cancer Society. Unfortunately, Jean VanderPyl was unavailable, so Gerry Johnson (Betty) stands in for her, while Betty doesn't have any lines of her own. Mel Blanc voices not only Barney, but the doctor.

Edit, 2/7/23: Had to change to a shorter video, so the doctor has been edited out.

If you recall the Busch Beer ad that was produced roughly around the same time, Johnson subbed for VanderPyl as Wilma then, too. Very rare in and of itself.