Gregory 'Greg' Pratt (recurring character at the end of Season 8). Mekhi Phifer joined the cast in Season 9 as Dr. Susan Lewis when Sherry Stringfield reprised her role after having left the series in Season 3. Season 8 saw the arrival of Sharif Atkins as medical student (later Dr.) Michael Gallant, as well as the return of Dr. Soon after, Maura Tierney was added as Nurse (later Dr.) Abigail 'Abby' Lockhart. Jing-Mei 'Deb' Chen, reprising a recurring character she portrayed in Season 1.

Dave Malucci, and Ming-Na returned to the series as Dr. A bit later in the season Erik Palladino joined as Dr. Robert 'Rocket' Romano (recurring character in both Seasons 4 and 5), Croatian actor Goran Visnjic as Dr. Season 6 opened with the addition of Paul McCrane as Dr. George Clooney's departure towards the end of Season 5 started a major cycle of main cast changes over the next few years. Season 5 saw the addition of Kellie Martin as medical student Lucy Knight. Anna Del Amico (recurring character at the end of Season 3) and Alex Kingston joined the cast as Dr. In Season 4, Maria Bello signed on as Dr. Kerry Weaver (recurring character in Season 2). The first additions to the main cast came in Season 2 with Gloria Reuben signing on as Physician Assistant Jeanie Boulet (recurring character in Season 1), and in Season 3 with Laura Innes as Dr. Julianna Margulies guest starred in the pilot as Nurse Carol Hathaway before becoming part of the regular cast. Susan Lewis, Noah Wyle as medical student (later Dr.) John Carter, and Eriq La Salle as Dr. Douglas 'Doug' Ross, Sherry Stringfield as Dr. The original starring cast consisted of Anthony Edwards as Dr. 2.6 Secondary doctors and medical students.2.3 Fire fighters, paramedics, police officers, and social workers.2.1 Desk clerks and other non-medical hospital staff.

Er season 1 cast and crew