In this episode, Black aids in the search for a man who is supposedly carrying a highly contagious virus and discovers the secret behind the Human Genome Project.
Johannessen has described "Sense and Antisense" as having suffered from extensive script re-writes; his original version dealt more strongly with racial issues but was rewritten at the behest of the network's broadcast standards office.
Millennium Group consultant Frank Black (Lance Henriksen) attends a briefing on the situation, where it is explained that Zero is carrying an exotic disease ordinarily confined to the Congo.
Meanwhile, Zero and Knox are attempting to have a local newspaper run Zero's story, believing he has been infected in a racially motivated conspiracy akin to the Tuskegee syphilis experiment.
Black realizes he was tricked into finding Zero for an ulterior motive, eventually learning that the organization responsible is carrying out medical experiments on the homeless and may be tied to the Millennium Group.
Watts and Black theorize that the Department of Energy is developing a biological weapon which would incite violence and rioting in a targeted population; they learn that the research is being conducted by scientists involved in the Human Genome Project.
Black believes Kramer was accidentally infected and finds a photograph in his office, showing him in military uniform, taking part in the 1994 Rwandan genocide.
Darin's music has been noted by Millennium's resident composer Mark Snow as a hallmark of the works of executive producers Glen Morgan and James Wong, and would also appear in the episodes "Beware of the Dog", "Monster", and "Goodbye Charlie".
[11] Robert Shearman and Lars Pearson, in their book Wanting to Believe: A Critical Guide to The X-Files, Millennium & The Lone Gunmen, rated "Sense and Antisense" two stars out of five, describing it as "too thin and too obvious".