One hundred and forty tons of snow and ice were trucked into a soundstage to create the scene with the submarine toward the end, and the stage had to be refrigerated for five days.
Steven Williams (Mr. X) and Mitch Pileggi (A.D. Skinner) improvised their famous elevator fight scene on the spot. During the filming of the sequence, Williams actually broke a knuckle on his right hand when he accidentally punched Pileggi. When Rob Bowman was dissatisfied with the first take of Skinner slamming X against the wall, Pileggi did it again with such force that the fake wall broke.
This is the first time Scully is shown getting into Mulder's apartment by way of a key on her own key chain.
This was the first episode of the series written by Frank Spotnitz. He would later become a collaborator on many mythology-centric episodes, and a co-writer on the two ''X-Files'' feature films.
The decommissioned submarine that features prominently in this episode was also used in the previous instalment Colony (1995) and a later episode Død Kalm (1995).