The Gang is in science class where they witness the binary fission of a bacterium. Gus is horrified when he finds out that bacteria and germs are the same thing, and believes that all germs can cause decay and disease. Mikey begs to differ, saying that bacteria and germs are living creatures and even gives each germ an individual name. As Mikey is about to release the germs, Gretchen makes the problem worse by informing Gus that germs are everywhere, causing him to run out of the classroom in a panic.
In the boys' room, the paranoid Gus is shown cleaning himself. At Recess, he shows up wearing a biohazard suit protecting him from germs. T.J. now realizes that Gus is overreacting, as Gretchen tries to clear up a few misconceptions, before suddenly starting to feel ill; she has caught a cold. It serves as a big deal to Gus who is convinced that the germs made her sick.
Gus is wandering round the playground in his suit, spreading the word about germs and frightening the Ashleys, when Menlo arrives, agreeing to help Gus in his anti-germ campaign, and putting on his own biohazard suit.
Gus holds a meeting in the playground discussing the dangers of germs, which Mikey observes atop Old Rusty. With nearly all the students joining Gus' campaign, Mikey decides to speak out for germs, but is jeered at by the students. Soon enough, they are cleaning up the playground and donning masks and surgical gloves, and a couple of tanker trucks arrive to disinfect the area of germs. Mikey decides to protest by holding up degermification, and refuses to budge. This only leads to a furious tussle between the two, which results in Mikey dropping his slide and breaking it. Believing that Gus killed the germs, Mikey becomes furious with him and the two start a big fight, which continues for some time until Gretchen arrives, having recovered from her cold.
Gretchen rekindles Gus and Mikey's friendship by saying that germs are neither good nor bad and they are just a part of life. Gus and Mikey both make up for earlier, and Gus happily re-opens the playground.
- This episode marks the first time a member of the gang is shown sick from school for a majority of the episode, this one being Gretchen. T.J. was mentioned to be sick for a week at the beginning of "Economics of Recess", however this was before the events of the episode.
- This is the only episode when Mikey hits somebody on purpose.
- This episode was cut in the Italian dub.
- This episode shares the same title as an episode of Dinosaurs, also produced by Walt Disney Television.
- This episode is similar to the Hey Arnold! episode, "Sid and Germs."
- This episode is "Lost" from the Latin American dub.
- T.J. Detweiler - Andrew Lawrence
- Vince LaSalle - Rickey D'Shon Colins
- Ashley Spinelli - Pamela Segall-Adlon
- Gretchen Grundler/Ashley Tomassia - Ashley Johnson
- Mikey Blumberg - Jason Davis
- Gus Griswald - Courtland Mead
- Miss Finster - April Winchell
- Ashley Armbruster/Kid #3/Kid #5 - Anndi McAfee
- Ashley Boulet - Francesca Smith
- Ashley Quinland - Rachel Crane
- Hustler Kid - Michael Shulman
- Menlo - Blake Ewing
- Erwin Lawson - Erik von Detten
- Gordy - Sam Gifaldi
- Kid #1 - Klee Bragger
- Kid #2 - Kath Soucie
- Kid #4 - Justin Shenkarow
- Kid #6 - Aria Noelle Curzon
- Man - Gregg Berger