The subway scenes were filmed at the World Trade Center PATH Station which was filling in for the Park Place Subway Station.
Leslie Denniston has appeared as five different characters over the course of the series:
- Episode 4.14 Censure (1994) - Sara Felder.
- Episode 5.16 Wannabe (1995) - Mrs. Prescott.
- Episode 8.17 Carrier (1998) - Lenore Kiley.
- Episode 12.3 For Love or Money (2001) - Elizabeth Dumas.
- Episode 16.14 Magnet (2006) - Ellen Loomis.
Charlie Hofheimer (Andrew Jameson) also played the role of Ben Karmel in Homesick (1996) (episode 6.22).
John C. Vennema played three different characters over the course of the series:
- Episode 3.5 Wedded Bliss (1992) - Victor Shay.
- Episode 5.16 Wannabe (1995) - Dr. Stephen Prescott.
- Episode 14.11 Darwinian (2004) - Dr. Aaron Geller.
Marin Ireland (Laura Booth) previously played the part of Anais Hutchinson in Zoonotic (2003) (episode 2.22).