The US hospital drama ER has flatlined, ending its run Thursday after 15 seasons on NBC.

The U.S.

Former ER staff George Clooney, Julianna Margulies, Noah Wyle and Eriq La Salle returned for one of the US hospital drama's final episodes Thursday night.

NEW YORK - Noah Wyle, the last continuous on-air link to the NBC medical drama "ER's" freshman season in 1994, seems headed for the doctor's retirement home. Wyle, who plays Dr. John Carter, told E! Entertainment Television on Thursday that he plans to leave the show at the end of this season.