Dr. Jekyll and Mr. Mouse is a 1947 one-reel animated cartoon and is the 30th Tom and Jerry short. The cartoon was released on 14 June 1947, and was directed by William Hanna and Joseph Barbera, produced by Fred Quimby and animated by Ed Barge, Michael Lah, Kenneth Muse and Al Grandmain. The episode is a parody of Dr. Jekyll and Mr. Hyde. It was nominated for the Academy Award for Best Short Subject: Cartoons in 1947, but lost to Warner Bros. Tweetie Pie.
Near a basement window are two milk bottles. Through the basement window, Tom reaches for one of the bottles and then snatches it, rushing into the living room to pour it in his bowl and drink it but Jerry also wants Tom's milk. Tom makes various attempts to catch Jerry but when they all fail, the cat dreams up a murderous plot to rid himself of his annoyance.
The next scene shows Tom mixing chemicals such as moth balls, acid, ammonia, and poison into his milk, upon mixing the deadly elixir, the chemicals cause the spoon to dissolve. After seeing a fly taking a little sip from the bowl before crying in pain and then dropping dead, Tom carefully carries the bowl and places it outside Jerry's hole, confident that his potion works, gleefully watching Jerry about to drink from the bowl.
Seeing the bowl of milk once again, the mouse drinks the milk, causing him to yell in pain and collapse "dead". Just before Tom can celebrate over the "dead" mouse, the full effects of the potion take place: Jerry starts to turn into a super-strong mega muscular version of himself who is now more than able to defend himself against the cat, only one thing is on Jerry's mind: REVENGE! With each thunderous step, Jerry takes the house shakes. Tom panics and shuts the door to the living room, but Jerry knocks it over. Jerry's seemingly infinite strength allows him to smack Tom against a safe, but the potion's effects wear off and Jerry returns to his normal size.
After realizing he can no longer pull the cat around, he dives away from the cat and into the milk bowl. Tom grabs the mouse out of the bowl as he screams and turns into the super-Jerry a second time, whom now grabs Tom and hurls him by his whiskers before the potion wears off. As Jerry realizes he is normal again he simply ties Tom's whiskers and tries to drink more potion. The feline upends the bowl with his foot before the mouse can drink enough, and the chase continues across the kitchen.
Once launching Tom into the kitchen refrigerator, Jerry hurriedly attempts to make more of the concoction himself, with a different formula but before Jerry has a chance to drink it, Tom escapes from the refrigerator and steals the milk from Jerry. The mouse tries to run away, but Tom stomps on his tail and forces his enemy to watch as he drinks the potion. The cat grins evilly at Jerry and as Tom grows to an enormous size. But then an explosion erupts from Tom, resulting him shrinking to a smaller size than Jerry.
For a second, both of them stare at each other. Then, Jerry realizes much to its delight that Tom is now smaller. Jerry grabs its tail from Tom's foot, causing Tom to lose his balance. Tom, terrified now, tries to run but Jerry holds onto Tom's tail and punches Tom's face. This triggers the cat to shrink more. Jerry then pulls Tom's tail and snaps it. Tom yells in a high-pitched scream and shrinks one last time all the way to the size of a fly, so Jerry decides to chase Mini-Tom with a flyswatter until the potion wears off.
- This is the third Tom and Jerry short to be nominated.
- Monster Jerry later reappears, decades later in the video game, Tom and Jerry in War of the Whiskers.
- The episode's title is a pun on Robert Louis Stevenson's book Strange Case of Dr.Jekyll and Mr.Hyde.
- A shot of the cartoon's original titles were found, but only in black and white. The original Technicolor version hasn't been found as of 2018. On October 7, 2018, a YouTube user cartoon98100 uploaded the full black and white titles of the cartoon taken from a 16mm Agfa print.
- This episode is similar to Mickey Mouse's episode The Worm Turns where Mickey creates a potion to make small person be strong.
- The book that Tom uses to hit Jerry is yellow on the shelf. When he grabs it, the book turns green.