<P> At this point, Rachel has run away from Jenn in St. Louis and is staying with Mark and Elizabeth . Though she vehemently denies it, her recreational drug use becomes apparent when her baby sister Ella gets hold of some ecstasy in her backpack and nearly dies after ingesting it in the episode "Damage is Done". When Rachel shows up, Mark can barely control his anger at her, berating her for repeatedly lying to him and for putting Ella in danger . However, he sees her remorse and fear for Ella are genuine; knowing Elizabeth is angry enough for both of them, he hugs Rachel when she starts to cry . When Mark refuses to throw Rachel out of the house, Elizabeth says she won't return home with Ella as long as Rachel is there and leaves home with Ella and moves into a hotel . Unwilling to tell Elizabeth about his condition, Mark stays with Susan during the course of his chemotherapy and radiation treatments . Elizabeth later finds out the truth and wants to come home, but Mark tells her she shouldn't pretend to be his wife just because he's sick; however, she returns anyway and begins helping Mark as his terminal illness advances . </P> <P> Eventually, however, he resigns himself to his fate and decides to halt the debilitating chemo, deciding he would rather have three good final months than twice that suffering from his treatments . On his last day in the ER, he meets with the same older woman that viewers saw on the first episode of ER . She again has a hangnail, and complains about how painful it is . Mark tells her that he has an inoperable tumor, asks another doctor to treat her, and tells the patient not to return to the ER again . He leaves the ER, stops his chemotherapy treatments, tells John Carter that he will now "set the tone" and takes Rachel on a last - minute trip to Hawaii to rebuild his relationship with her and relive happier times . </P> <P> After several moves around the island and some conflict with a surly Rachel, Mark suffers from increased symptoms, prompting Rachel to call Elizabeth, who comes to Hawaii with Ella . One night, Rachel comes to her father's room while he sleeps . Mark awakens and smiles at Rachel, telling her with slurred speech that he was just dreaming of her and how she used to love balloons . He tells her that he was trying to think of a piece of advice that every father should tell his daughter, and tells her to be generous with her time, her love, and her life . Rachel tells her father that she remembers a lullaby that Mark used to sing her when she was a baby and slips a pair of headphones on his head and plays Israel Kamakawiwo'ole's rendition of "Over The Rainbow" for him as he smiles and falls back asleep . While the song plays, he is seen walking through an empty ER . The next morning, Elizabeth discovers that he has died . </P> <P> In the episode "The Letter," Carter discovers two faxes that had arrived earlier, both sent by Elizabeth . He reads the first one to the staff . It is a letter that Mark had written about his sentiments about the Chicago County ER where he had worked for many years, and the staff he had worked with throughout the years . They begin happily discussing his letter until someone notices that Carter is holding the second fax, visibly upset . He informs them that the second is a brief letter written by Elizabeth, notifying them that Mark had died that morning around 6 A.M., "...at sunrise, his favorite time of the day ." She explains that she sent the first letter to show the staff at the ER what he thought of them . As the staff responds sadly to this news, Frank asks if he should post the second fax on the staff bulletin board, and Carter tells him to post both of them . The letter and the news of his passing sends many of the ER's staff that day into emotional turmoil, with Kerry Weaver going from second - guessing Abby's posting of the letter (she quickly changes her mind and says it should stay up) to crying and stating her regrets to Sandy Lopez that she's lost a friend . This portion of the episode closely models the scene at the end of the film Mister Roberts, when Jack Lemmon's character, Ensign Pulver, reads two similar letters connected with the title character's death . It was also revealed in the episode by Susan Lewis that he died at the age of 38, making his birth year 1964 . At the close of the episode, as the staff rush out to the ambulance bay to handle incoming casualties, the wind blowing through the open door tears one page of Mark's letter off the bulletin board . </P>

Song played when dr. green died on er