Dr Morgenstern left in Season 1 to take a job in Boston and was replaced by Dr Swift. In this episode, Morgenstern is back as if he never left. His return is not explained until episode 2x2 "Summer Run".
First appearance in the series of Ron Eldard, playing Carol Hathaway's new boyfriend, Shep. Eldard and Julianna Margulies were boyfriend and girlfriend in real life at the time.
Laura Innes' first appearance on the series as Kerry Weaver. She was originally hired to do six episodes.
In some of the exterior scenes, we see Carter and Benton walking outside in their surgical scrubs, covered in sweat. This is real sweat as it was filmed during a heatwave in Chicago. Even though just prior to the scene, both actors had been in air conditioning, the minute they stepped outside, they started sweating profusely. This caused problems for Noah Wyle, whose character was suntanned after a vacation. His tan (which was in fact make-up) kept dripping off. Edit: the AC was considered to be broken, hence the HVAC workers. The show is shot in LA, not in Chicago.