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Noah Wyle was the last member of the original cast to leave at the end of the 2004-2005 season. He appeared occasionally in later seasons. Sherry Stringfield is also an original cast member, but she left for five seasons, which made Noah Wyle the only cast member to be on the show every year for the series' first eleven seasons.
During an interview for the PBS series "Pioneers of Television," Noah Wyle said that while filming some of Carter's Africa storyline in the Kalahari Desert, the real on-set medic passed out from the heat, and Wyle (who by that time had been filmed pretending to perform hundreds of simulated medical procedures for the television show) inserted a real I.V. and hooked the medic up to a real saline drip.
Goran Visnjic named his character after the writers could not develop an appropriately Croatian name. The character is named for Visnjic's nephew (Luka) and his best friend (Kovac).
Frank, the desk clerk (Troy Evans), always talks about life on the "force" as a Chicago police officer. In the first episode, he had an appearance as a police officer who was shot and treated by the ER staff.
Although mostly shot at "Warner Brothers" Burbank soundstages, the cast and crew usually would make at least two trips to Chicago each season to shoot realistic exterior scenes for several episodes, which include many familiar Chicago landmarks. These scenes are typically shot on early Sunday mornings to avoid disrupting traffic.
Season 14 was supposed to be the final season, but the 2007-08 WGA strike left the producers and NBC without enough episodes to provide a proper final victory lap season. They agreed to return the show for the fifteenth and last season, which began in September 2008 and concluded on April 2, 2009.