- 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.
- Trigger is a collie mix instead of a cocker spaniel.
- The Beymer twins were omitted.
- Kathryn is not deaf.
- In the TV adaptation, the cat turns out to be a young witch who used to stay with Kathryn, but was almost thrown out for practicing witchcraft (which is what the Monster Blood is) until she used magic to turn herself into a cat.
- The ending is tweaked so that it ends on a cliffhanger, leading into "More Monster Blood".
|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.