- Kyle Labine as Evan Ross
- Sarah Podemski as Andy
- Corinne Conley as Aunt Kathryn
- Joy Tanner as Sarabeth
- Mark Benesh as Curtis
- Mark Melymick as Dad
- Janet Land as Mom
- Ashley Dawn Brown as Julia (uncredited)
During a stay at his weird Aunt Kathryn's, Evan is forbidden to enter one of her upstairs rooms. He just has to find out what's behind that door! But when he decides to take a peek, Evan finds more than he bargained for: an old, dusty can of "Monster Blood" that's green and slimy and starting to grow!
Differences from the book
- Evan and Andy find the Monster Blood in a room Kathryn forbid them from entering. In the book, they bought a can of Monster Blood at an old toy store. Additionally, the Monster Blood was simply a normal toy that Sarabeth cursed while in the episode she created it to begin with.
- Trigger is a collie mix instead of a cocker spaniel.
- The Beymer twins are omitted.
- Kathryn is not deaf in the episode, and is simply hard of hearing.
- In the TV adaptation, Sarabeth's backstory is elaborated on. She used to be Kathryn's roommate but was almost thrown out for practicing witchcraft until she was pushed into the monster blood she created.
- The ending is tweaked so that it ends on a cliffhanger, leading into "More Monster Blood". The book's ending is more conclusive, with Evan and Andy discovering that the Monster Blood is completely gone.
- Andy has less of her snarky personality in the episode.
|Title||Release date||Media type|
|September 16, 2008||DVD|
|August 26, 2014||DVD|
- This episode is a part one of a two part hour special, with the second part being "More Monster Blood", unrelated to Monster Blood II.
- According to the script, the episode was orginally going to open with the scene of Evan and Andy trying to stop the growing Monster Blood before flashing back to how everything started. 
- For some unknown reason, "Monster Blood" and "More Monster Blood" were not released on DVD in the initial 2005 releases. What's even stranger is that the original 1992 cover art for Monster Blood was used for the DVD release of "Chillogy" instead. This would also be changed later on to the cover art for Monster Blood III.