By the time they were through, Abbott and Costello got to mix it up with just about all of Universal Studios' iconic monsters; here they take their mayhem over to England to exchange pleasantries with Boris Karloff and his portrayal of Dr. Jekyll and Mr. Hyde. Karloff has a turn at a variation of the Wolfman gimmick, becoming the Hyde monster whenever he injects himself with a drug designed to do just that. He's been experimenting with concoctions that turn people into animals, and before it's all over, Lou Costello winds up as a large mouse and a derby wearing version of Hyde himself.
As in many of their films there's also a romantic angle, this time with Helen Westcott and Craig Stevens doing the honors, to the consternation of Dr. Jekyll. Vicky Edwards (Westcott) has been Jekyll's ward since childhood, and he fancies himself a candidate to be her husband. This MayDecember match up is not going to work, so Jekyll figures to make things rough for Bruce Adams (Stevens) in the romance department. The London police department is turned on it's ear in search of monsters showing up all over the city after Tubby (Lou) takes a syringe full of serum.
Having seen this film many years ago as a kid, the one bit I remembered best was the rooftop scene with Slim (Bud), Adams, and the two Mr. Hydes doing the gag around the chimney. It was just one of the many scenarios requiring orchestrated timing, a hallmark of their comedies.
This was Abbott and Costello's second screen pairing with the legendary Boris Karloff, the first time was in 1949's "A and C Meet the Killer". Oddly, Karloff did not reprise the role he created for "A and C Meet Frankenstein", believing that spoofing his creation wouldn't sell audiences. Even in the Jekyll and Hyde movie, he seems to carry an air that wants to rise above the slapstick. For Bud and Lou though, the gimmicks don't run out until the very end, when in the final scene the police inspector (Reginal Denny) and four of his men all become Hyde monsters after taking a "wolfman" bite from Tubby - Yikes!!
Review by classicsoncall from the Internet Movie Database.