GEORGE AND IZZIE'S ROMANTIC CHEMISTRY IS PUT TO THE TEST, MARK DEVELOPS A CRUSH ON A FELLOW SURGEON, AND CALLIE'S ROLE AS CHIEF RESIDENT IS IN JEOPARDY, ON ABC'S "GREY'S ANATOMY"

Jeff Perry Returns as Thatcher Grey

"Physical Attraction� Chemical Reaction" � George and Izzie's romantic chemistry is put to the test, as Derek asks for more than a physical connection from Meredith; much to his own surprise, Mark develops a crush on a fellow surgeon, and Callie's role as Chief Resident is placed in jeopardy after she delegates much of her job to Bailey, on "Grey's Anatomy," THURSDAY, JANUARY 24 (9:00-10:02 p.m., ET) on the ABC Television Network. (Rebroadcast. OAD 11/8/07)

"Grey's Anatomy" stars Ellen Pompeo as Meredith Grey, Patrick Dempsey as Derek Shepherd, Sandra Oh as Cristina Yang, Katherine Heigl as Isobel "Izzie" Stevens, Justin Chambers as Alex Karev, T.R. Knight as George O'Malley, Chandra Wilson as Miranda Bailey, James Pickens, Jr. as Richard Webber, Sara Ramirez as Callie Torres, Eric Dane as Mark Sloan, Chyler Leigh as Lexie Grey and Brooke Smith as Erica Hahn.

Guest Cast: Jeff Perry as Thatcher, Rockmond Dunbar as Sean, Stephanie March as Jane, Vicki Lewis as Harriet, David Burke as Don, Kurt Fuller as Jerry and Enuka Okuma as Teresa.

"Physical Attraction� Chemical Reaction" was written by Tony Phelan and Joan Rater and directed by Jeff Melman.

"Grey's Anatomy" is broadcast in 720 Progressive (720P), ABC's selected HDTV format, with 5.1-channel surround sound and Spanish audio via SAP. This program carries a TV-14,D,S parental guideline.

This episode of "Grey's Anatomy" will be available on ABC.com the day after airing on the network for users to watch online.