The end is near for Dr. Mark Greene, one of the most popular characters on the most watched medical drama in TV history.

But that doesn't seem to faze the makers of ER

In all its years as TV's most-watched drama, the show has barely missed a step when its top docs and nurses traded in their stethoscopes for film careers. 

Among the ER dearly departed are Hollywood heavyweights George Clooney, William H. Macy and Julianna Margulies. 

But by the end of next month, the show will have lost one of its most well-liked characters Dr. Mark Green (Anthony Edwards) as well as Dr. Peter Benton (Eriq LaSalle). Both have been cornerstones of the show since its 1994 pilot. 

Filming "the last show with [Edwards] was definitely bittersweet," says executive producer Jack Orman. "He's a lot of the reason why the show's the success that it is." 

The cast and crew finished filming the show's eighth season last Friday. 

And for the first time in years ER been feeling the heat from another popular show gunning to steal away the crown as TV's most watched drama. 

CBS' hot crime drama CSI has for a few weeks this year snared the top spot on the Nielsen lists, and with the show's audience growing each week, next season is shaping up as a battleground. 

"We don't change the way we do anything . . . because of that," Orman says. 

With Edwards and LaSalle gone, the only original cast members left next fall will be Noah Wyle (Dr. John Carter) and Sherry Stringfield (Dr. Susan Lewis) who actually left the ER after its second season and returned this past season. 

But Orman says even the newer actors on the show feel like they've always been there. 

"I think Maura Tierney, Goran Visnjic and Alex Kingston all feel like they've been on the show a long time and people tune in to see them." 

Those three  especially Tierney, who joined the cast last year got lucky during the show's seventh season (2000-2001) in that it was one of the few years in ER history that someone important didn't leave the show, Orman said. 

"We had a certain stability in that cast last year and there was a comfort level there," he says. "We knew we had a cast that was with us for the season and we could develop some of the newer characters." 

Tierney was one of the biggest beneficiaries producers paired her with Sally Field, who won an Emmy for her guest starring role as the mother of Tierney's character.

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