Well fear gas doesn't effect Joker and Scarecrow doesn't have any emotions as in Love, or Humor.
Does Joker's Laughing Gas effect Scarecrow?
@xerox_kitty: Uh this is a comic book. Not real life, so laughing gas is somewhat different from Joker compared to like a dentist.
Still Jokers laughing gas does not work on emotion. It is just a chemical that makes your body laugh and die, not make you laugh out of happiness.
Remember, though, that Scarecrow is fairly often defeated by being gassed with his own fear toxin. It happens less often in the comics than it does in film and TV shows, but it happens and he is affected. If he would be immune to any toxin, it would be his own, and he's not immune to that.
We haven't seen Joker gas Scarecrow recently, at least not since Scarecrow became deadened to all emotion (although I agree with most people here that Joker's toxin isn't usually portrayed as actually affecting emotion).
However, there was a short-lived Joker comics series in 1975 and '76. It only lasted nine issues, but in #8, Joker and Scarecrow were fighting and it ended with Joker gassing him with a non-lethal variant of his trademark toxin as he thought Scarecrow was being too much of a fuddy-duddy. This gas did affect Scarecrow, who was left giggling foolishly for law enforcement to pick up.
But keep in mind that the idea that Scarecrow doesn't experience any emotion is a fairly recent development. What's more, we haven't seen if it applies any more in the new DC reboot universe.
I have no clue about the Scarecrow being immune to Joker toxin, and I don't know if it's cannon or not, but I do remember reading either in a DC book or on his page on here that Joker is immune to most toxins and poisons, including Scarecrows toxin.
This edit will also create new pages on Comic Vine for:Beware, you are proposing to add brand new pages to the wiki along with your edits. Make sure this is what you intended. This will likely increase the time it takes for your changes to go live.