You Look Familiar: Before playing Sarah Mackenzie, Catherine Bell played a Navy Lieutenant love interest of Harm's who died in the (intended) first season finale. Harm notices this, and is visibly stand-offish towards her at first because of it. In real life, Bell all but begged to be brought back on the show as another character, and the two characters looking identical was utilized.
Mac: Sounds like I have a twin out there.
Harm: Not anymore.
- Another example is with Lt. Loren Singer, whose actress played an assassin in an earlier episode. This, along with Bellisario's kids showing up, suggests a little nepotism, as David James Elliot (Harm) and Nanci Chambers (Singer) are married in real life.
- Also, Alexander Kuznetsov appears first in "Cowboys and Cossacks" as Commander Kretchiak, and in later episodes as a different Russian officer named Captain Alex Volkonov (who becomes Harm's Russian analogue throughout the series).
- John Walcutt once played a defendant, Caleb Farmer, who was put to death for his crimes, with Mac defending him and Harm prosecuting. Later, he would come back to play Tom Johnson father of the young girl Harm had befriended and seeking to be her legal guardian.
- Barry Jenner (Dallas, Star Trek: Voyager) first appeared in "Ares" as the captain of an Arleigh Burke-class destroyer, and later in "Mr. Rabb Goes to Washington" as the asshole ZNN reporter Norman Delaporte.
- Jerry Hardin (Deep Throat in The X-Files) first appears as an airplane mechanic in "Full Engagement", and as a Senator in "Impact" (the latter a UFO-themed episode no less).