"Tainted Obligation" is the fourth episode of the sixth season of Grey's Anatomy and the 105th produced episode of the series. It is also the 138th produced episode of the Grey's Anatomy franchise. It was broadcast on October 8, 2009.
When Meredith and Lexie's father Thatcher returns to the hospital with a failed liver Meredith is unsure of how to feel but, when Lexie isn't a match for a liver transplant, Meredith faces a crisis when Lexie begs her to come forward and save their father. Izzie emphasizes with a patient riddled with tumours while Alex grows tired of his current living situation. Mark, annoyed with Cristina's competitive zeal, tricks her into assisting on an unusual surgery and Arizona urges Callie to beg the Cheif for her job back.
- "We begin life with few obligations. We pledge alliegence to the flag, we swear to return our library books. But as we get older we take vows, we make promises, we get burdened by commitments: to do not harm, to tell the truth and nothing but, to love and cherish to death do us part. So we just keep running up a tab until we owe everything to everybody and suddenly thing: what the-"
- "The thing about being a surgeron is everyone wants a piece of you. We take one little oath and suddenly we're drowning in obligations; to our patients, to our colleagues, to medicine itself. So we do what any sane person would do: we run like hell from our promises hoping they'll be forgotten. But sooner or later, they always catch up. And sometimes you find the obligation you dread the most isn't worth running from at all."
- "Trading Things In" - The Voluntary Butler Scheme
- "Come On, Be Good" - Dragonette
- "Long Gone Time" - Bachelorette
- "Wish You Well" - Katie Herzig
- "Morning Mist" - Sebastien Schuller
This episodes' title references the song Tainted Obligation, originally sung by R.E.M