The exterior shot of the asteroid which USS Voyager goes in to chase the Vidiian ship is the exact same exterior shot of the asteroid where the Enterprise-D locates the USS Pegasus in The Pegasus (1994)
This is the first of several times The Doctor uses the phrase "I'm a doctor, not a _______", a catchphrase that was made famous by Dr. McCoy in Star Trek (1966).
In this episode the term 'phage' is used for a virus that attacks animal cells. 'Phage' is short for 'bacteriophage', a virus that specifically infects bacteria and archaebacteria.
The subterranean Vidiian corridor was a reuse of the hidden corridor that crew members find behind a holographic barn in Caretaker (1995).
Because the aliens of this episode were originally collectively named Vaphorans, Dereth clearly mouths the word "Vaphoran" in Voyager's transporter room; evidently, "Vidiian" was subsequently looped over it. Broadcast closed captions of this episode also use "Vaphoran". The change from that collective term to "Vidiians" was made when it was realized that no two performers could pronounce "Vaphoran" in the same exact way.