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Smylex was the Joker's code name for his poison that left frozen grins on its victims. It appeared as green or sometimes purple vapor, usually causing people to spasm and laugh uncontrollably.

The Joker later laced random ingredients to hygiene products with components of Smylex. When certain hygiene products were applied in specific combination, they would fall victim to the poison.


DDID Nerve Gas[]

Jack Napier, after becoming the Joker, kept a stolen CIA file on his desk at Axis Chemicals. How Napier obtained the folder is not definitely known; presumably, Axis Chemicals was likely a Pentagon contractor. However, the file contained information about, and photos of test subjects for, an experimental nerve gas known as "DDID." A "persistent" nerve gas (effective for ten minutes or longer, unlike most nerve gases) used to kill, as nerve gases are generally used, it was discontinued in 1977 as it caused victims to violently convulse, with their facial muscles pulled taut in a rictus grin. It was likely deemed a violation of the Geneva and BWC protocols. The Joker spread hundreds of photos of poisoned soldiers on the floor of his studio room.

Using the aptitude for chemistry he had already shown while he was still simply the hoodlum Jack Napier, the Joker commenced to concoct his own custom version of the poison that would cause uncontrollable laughter before death. To that end, he worked with a scientist employed at the facility on finding a way to distribute it in the raw chemical component products shipped from Axis.

Smylex Commercial[]

The Joker taped a taunting "commercial" that would interrupt an Action News report breaking the first news of its victims, models Candy Walker and Amanda Keeler. Photos of both of the models, with super-imposed lips saying, "Love that Joker!" accompanied him in the commercial. A live, unpoisoned, gagged and bound hostage was seen in the tape next to an unidentified male corpse suffering the effects of Smylex. Elaborate sets and faux Smylex product props were made by the Joker's men for the threatening video. Asking the rhetorical question, "How do I get these products?" (though he did not so phrase it exactly) in the "commercial," the Joker said as if in answer, "Well, that's the gag. Chances are, you bought 'em already!"

Incident at the Flugelheim[]

Purple Smylex

The Joker began to spread terror in the city, first by lacing hygiene products with a deadly chemical known as "Smylex," which caused victims to laugh to death when it was used in certain combinations. The Joker then set a trap at the Flugelheim Museum for photojournalist Vicki Vale, and he and his Goons vandalized the surrounding works of art over the corpses of poisoned civilians. Batman arrived soon after, rescued Vicki, and the pair escaped in the Batmobile. Inside his "headquarters," the Batcave, after pointing out that the police were mistaken in seeking only one product and that the Joker had actually tainted hundreds of basic chemicals at the source, Batman gave information about Smylex to Vicki so that she could warn the city via the press about the poisoned products, though he seized film she had shot that showed him at least partially unmasked and, indeed, at all. Alexander Knox was the first to break the story in print, with a front-page story on the Gotham Globe under the headline, "Batman Cracks Joker's Poison Code!"

200th Anniversary Parade[]

Batman 1989 - Joker Goons at Festival 2

Batman later used his communicator to send the Batmobile into the Axis processing plant to drop an explosive. This resulted in a large series of chain-reaction explosions that destroyed the source of the poison. But the Joker taunted Batman from his green helicopter to claim that Batman had accomplished little, and that the parade was still on.

Meanwhile, the Joker's army of goons had amassed at the 200th Anniversary Parade with a promise to give away $20 million in cash. When the citizens arrived, however, the Joker instead attacked them with Smylex gas spewing from the inside of his giant balloons. Batman arrived on the scene and saved Gotham from the attack by using the Batwing, pulling the balloons away from the crowd.

This chemical weapon was never seen again in the city.

Known Victims[]


Other Appearances[]

Arkham Game Series[]

As seen on gas-canisters in the games, Joker's laughing gas is canonically referred to as Smilex.

The Lego Batman Movie[]

While not appearing directly in the film, Harley Quinn is wearing a t-shirt which says, "Smylex" on it.

Behind the Scenes[]


  • This chemical weapon was based on the DC Comics's "Joker Venom," the Joker's chief weapon, and any other alias for the poison that left the Joker's victims with a post-mortem rictus grin.
  • In Sam Hamm's original script, the first time that we saw Smylex's effect (called Smylenol in the script) was on the two female models, who were only represented as cardboard cut-outs in Joker's commercial. The original scene had them in a bikini photo session with a photographer. The photographer urged them to smile more as he snapped away. The girls began to giggle, which at first pleased the photographer. Soon, their giggles became laughter before they became uncontrollable helpless hysterics, which had the photographer going from mild annoyance to complete horror as the exhausted girls expired from forced hilarity, with the ghastly Joker-like grins that were frozen on their faces.
  • As it was originally intended, the death scene was much more protracted than the one with the female newscaster, which depicted death by Smylex as a particularly agonizing, if mirthful, way to go.
  • In the novelization of the film, the photographer was revealed to be Vicki Vale.
  • In the 2005 film Charlie and the Chocolate Factory, directed by Tim Burton, who had also directed Batman and Batman Returns, Smilex is the name given to a brand of tooth-paste as an easter-egg to Burton's history with Batman.