Alive and kicking at 200, ER shows no signs of slowing.

The medical drama that turned all tubers into unofficial med students, teaching us how to pronounce hospital jargon (repeat after me, myocardial infarction) and how to jump-start a patient's heart with a defibrillator, celebrates its landmark anniversary with healthy ratings and a special episode tonight that spans 24 hours in the ER.

As usual, there will be blood, lots of it, an overcrowded emergency room at County General and doctors on the verge, as Dr. Carter treats two cult victims from a mass poisoning stemming from that day's solar eclipse, and Dr. Gregory Pratt (played by Mekhi Phifer) tackles an intensive night shift in the episode titled "When Night Meets Day."

Welcome to the ER.

Ten years ago, no one expected the series to pull through. First conceived as a screenplay by medical student turned writer Michael Crichton more than 20 years ago, it took the collaboration of Hollywood heavyweights Steven Spielberg, John Wells and Crichton to bring the show to the air. Even so, NBC was hesitant about a gritty medical drama that moved fast, used complex medical terms and unmasked its doctors as less than God-like. The Peacock also had to contend with CBS' rival series, Chicago Hope, created by David E. Kelley.

Prognosis negative.

However, when the two-hour pilot aired September 19, 1994, viewers checked in to County almost immediately and never checked out. By midseason, it was the number-one show, and since then, ER has consistently ranked in the top 10, while Hope settled into the top 30 and was canceled in 2000. This season, ER ranks fourth, over scrub sensations American Idol and Survivor, drawing an average 19.9 million viewers per week, according to Nielsen Media Research.

The positive response surprised even executive producer Wells. "It surpassed my expectations when it was picked up from the pilot to be on the fall schedule," said Wells at a recent press conference. "It's been a wonderful thing, but I'd never before been involved with something that became quickly such a part of the overall culture," he added, referring to a Newsweek cover and a Saturday Night Live parody.

Through it all, Noah Wyle as Dr. John Carter has remained the one constant, going full circle from med student to mature physician. Which was sort of the point, according to Wells. "The series is always about the growth of this medical student," who would ease viewers into the technical lingo and medical procedures, said Wells, who envisions Carter managing the ER by the series finale.

Wells' wish could come true. Wyle has stuck around through nine seasons and claims his "commitment to the show is as strong as ever." This was not the case for the dozens of castmembers who've passed through County's doors over the years.

The first actor hired to wear doctor's whites on ER was George Clooney, the equivalent of TV ipecac at the time. Before Ocean's Eleven, The Perfect Storm and Dr. Doug Ross, Clooney was a B-list actor probably best known as a recurring character on The Facts of Life. His credits included a list of failed pilots, among them an ill-fated sitcom called E/R.

Now, Dr. Ross is considered County General's most successful alumni. Of course, that hasn't stopped other castmembers from attempting to trade in their scrubs for red-carpet glamor. Other original castmembers who handed in their resignations include Julianna Marguilies (Nurse Hathaway) who most recently appeared in Ghost Ship; Eriq LaSalle (Dr. Peter Benton) who starred in this year's Biker Boyz; Anthony Edwards (Dr. Mark Greene) who's shooting a big-screen adaptation of the marionette series The Thunderbirds and Sherry Stringfield (Dr. Susan Lewis) who returned to the hit series in 2001 after a five-year absence and a string of straight-to-video stinkers.

Along the way, the show has also welcomed a revolving door of special guest stars, including Sally Field as Abby Wyczenski Lockhart's (played by Maura Tierney) bipolar mother, Don Cheadle as handicapped doctor Paul Nathan and Alan Alda as a doctor afflicted with Alzheimer's. "Getting the opportunity to work with Alan Alda is one of the highlights of my career," said Wyle, adding, "He was a hero to me growing up. He still is."

All due respect to the good doctor Alda (aka M*A*S*H's Dr. Hawkeye Pierce) but Wyle has also come a long way since his days as a trust-fund kid and an inept resident who couldn't draw blood. "I supposed the thing I really enjoy is the comfort and ease that medical dialogue and procedures come to me," admitted Wyle, adding, "Very rarely does an actor get to play the flip side of the character that he started with."

Among the perks of being the ER's most experienced doctor, Wyle's tenure also earns him an estimated $400,000 per episode. Then there's the recent trip to Hawaii with fellow castmember Goran Visnjic, who plays Dr. Luka Kovac. The tropical island subs in for the African Congo where the two doctors travel to treat victims of a civil war. The two-part cliffhanger serves as both the series finale, airing May 15, and next season's opener.

As for when Wyle & Co. will hang up their stethoscopes, Wells concedes the series can't live forever, but he has no plans of pulling the plug just yet. "I think we're heading into what I assume will be the last few years...Whether that's three years or four years or two years, I'm not sure."