Lurking... is played in E2M2, E2M6, E5M2, E5M6 of Wolfenstein 3D (DOS).
The song is track number 19 in the game's data. Its title in the IMF meta data is "PREGNANT". It is not included in the shareware version of Wolfenstein 3D. The name is verified by in-game jukebox.
This song was composed with Sequencer Plus Gold.