In a hilarious send-up, Clooney reprised his role as Dr. Doug Ross from the first five seasons of the hit NBC show, while host Jimmy Kimmel played a patient who had "lost a lot of blood."
"Somebody, bring me a scalpel," Clooney calls out during the skit.
But when no one comes running, Kimmel confesses that the "ER" reunion he planned isn't going to be much of a reunion.
"I know I'm supposed to be under, but the reason nobody's bringing you a scalpel is because this was kind of a last-minute thing and we had some trouble getting the whole cast of 'ER,'" he says.
"Julianna Margulies?" Clooney asks.
"She's filming 'The Good Wife' so she couldn't make it," Kimmel replies.
"Noah Wyle?" Clooney asks.
"He wanted to be here," Kimmel says, "but I guess he's got a thing with his family: Taco Tuesday."
"Eriq La Salle?" Clooney inquires.
"Oh, no. Eriq La Salle has jury duty," Kimmel says. "I'm sorry. We really probably shouldn't have even done this. If you want to cancel, because we can ..."
But Clooney refuses to back out, saying, "When George Clooney says he's going to show up for an ‘ER’ reunion, George Clooney does it."
Then he asks Kimmel whether he has anybody. That's when Hugh Laurie from "House" shows up.
After sussing out the problem, the two prepare to operate when Kimmel goes into "multisystem organ failure." Clooney performs CPR but that still doesn't work. That's when Laurie suggests giving him the "rapper's delight."
"Aw, Dr. Ross," Laurie says. "Do you remember what they taught us at TV medical school?"
Clooney then breaks into the Sugarhill Gang's 1979 hit "Rappers Delight," bringing Kimmel back to life.
"Dr. Ross, you saved him!" Laurie tells Clooney. "You used hip-hop to save this man's life. Dr. Ross, you're a genius."
Check out Dr. Ross saving Jimmy Kimmel below: