"ER" is headed into the sunset this coming season, but the show is still adding new blood to its cast.

Four actors -- Shiri Appleby, Emily Rose, Julian Morris and Victor Rasuk -- will join the NBC series for its 15th and final season as new interns at County General. Another NBC show, "Knight Rider," has added Paul Campbell to its cast, according to The Hollywood Reporter.

The four "ER" actors will all have recurring parts. Appleby ("Six Degrees," " Charlie Wilson's War") and Morris ("Cry Wolf") will play siblings, she a willing learner and he a charmer who uses his looks to get by.

Rose ("Brothers & Sisters") will play a control freak who buts heads with her superiors, and Rasuk ("Stop-Loss") will play a newlywed who's often on the phone with his wife.

"The new group of young characters ... adds a burst of fresh energy and a bunch of different personalities for us to play off of as we enter our 15th and final season," executive producer David Zabel says. "While we will be reconnecting with the history of 'ER,' as well as telling the ongoing stories of our current regulars, we also will track the development of these new young doctors."

On "Knight Rider," Campbell is set to play a research technician at Knight Industries, which built and maintains supercar KITT. Campbell's credits include "Nobody's Watching" and "Battlestar Galactica."