'ER': Countdown to the series finale

After 15 seasons and 331 episodes, NBC's beloved medical drama "ER" will say its good-byes this Thursday (April 2). Original cast members have come, gone and come back again, but fans still can't get enough.

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The Episodes:

The Los Angeles Times takes a look back at three memorable episodes that will stick with them forever.

    The Pilot: '24 Hours'
    Season One: 'Love's Labor Lost'
    Season Six: 'Be Still My Heart'

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'ER': 15 years, 15 casts -- From the original staff of SherryStringfield, Anthony Edwards, Noah Wyle, Julianna Margulies, George Clooney and Eriq La Salle to Season 15's Linda Cardellini, Scott Grimes, John Stamos, Parminder Nagra, David Lyons and Angela Bassett.

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Emmy-nominated guest stars -- Merely dropping by the "ER" had perks of its own. Both big-name and character actors picked up an Emmy nomination when they visited, including Ewan McGregor, William H. Macy, Swoosie Kurtz, Alan Alda, James Cromwell, Sally Field, Mary McDonnell, Don Cheadle, Bob Newhart, Ray Liotta, James Woods and Forest Whitaker.

Animals

'ER's' animal antics: Animal guest stars -- People weren't the only ones who showed up in the "ER" looking for medical attention. Other patients included a camel, chimpanzee, shark and miniature pony.

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'ER' essay -- The Los Angeles Times ruminates how over 15 seasons, the place has changed from a literal emergency room into a metaphor of crisis where every triumph is temporary because another disaster is on the way..

Finalrounds

On the 'ER' set: The final rounds -- On the last day of filming, cast members get nostalgic and reveal what working on "ER" has meant to them.

Finally, get ready to say good-bye with the video below and see clips from the series finale as well as memorable moments from seasons past.