*Oprah Winfrey is marking the 50th anniversary of the first Freedom Ride and this month’s remarkable PBS documentary about the movement by featuring 178 former Freedom Riders on Wednesday’s broadcast of her talk show.

Harpo Productions says it’s one of the largest gatherings of Freedom Riders since 1961. The riders peacefully opposed 1960s racial segregation of the South.

Winfrey says she owes “a deep debt of gratitude” to the Freedom Riders. She says she knows her “life would be different were it not for them.”

Guests on the show are to include U.S. Rep. John Lewis of Georgia and John Seigenthaler, who was assistant to then-U.S. Attorney General Robert Kennedy. Both men were beaten during the civil rights movement.

The episode is to be among Winfrey’s last. “The Oprah Winfrey Show” ends May 25 after 25 years.

PBS’s American Experience will premiere its OUTSTANDING documentary “Freedom Riders” on May 16. Watch a preview below.

Watch the full episode. See more American Experience.