It involves ice and a bucket.
Lady Gaga has done it. So have Jon Bon Jovi, Taylor Swift, Charlie Sheen, Justin Timberlake and Gwen Stefani.
Even the Facebook man himself, Mark Zuckerberg, has done it.
Justin Bieber did it twice after being called out the first time for forgetting the ice.
Selena Gomez has joined the list - and there was plenty of ice in her bucket.
Celebrities are putting their fame to good use by taking on the Ice Bucket Challenge, which raises awareness and money for the fight against Lou Gehrig’s disease.
They are being nominated by famous friends to take on the icy bucket blast or donate to charity. Most stars are doing both.
The campaign has been a big boost to charities connected to Lou Gehrig’s disease - a motor neurone disease known as amyotrophic lateral sclerosis (ALS)– more than $14 million has been raised and there have been more than 1.2 million bucket challenge videos posted on Facebook.
The Ice Bucket Challenge has become a viral craze in the United States with Lady Gaga the latest big name to accept the challenge.
Gaga, in Perth this week to perform at Perth Arena tomorrow, posted a video on her social media accounts last night showing her taking the challenge.
The video shows her pouring ice from a silver bucket over her head as she sits on a chair wearing nothing but a skimpy black outfit and black lipstick.
And she doesn’t flinch.
She posted the video to Instagram and nominated other celebrities to take the challenge: “#IceBucketChallenge #ALS #SharePainShowCompassion I nominate Adele, Michael Rapino, Vincent Herbert, and Arthur Fogel #RichPeople (sic).”
“I also nominate @bobby_campbell and the cast of @ChicagoFire.”
Stars such as Jon Bon Jovi, Carrie Underwood, Justin Timberlake, Eddie Vedder and Gwen Stefani also joined the challenge at the weekend, posting videos online of their chilly water moments.
Vedder took the task on after Pearl Jam bandmate Mike McCready called on him and the rest of the group to join him.
Vedder nominated pal Bruce Springsteen, One Direction star Niall Horan and actor Tim Robbins.
Hollywood actor Charlie Sheen showered himself in dollar bills after swapping an ice bucket for a pail full of cash for charity.
The former Two and a Half Men star threw $US10,000 ($10,820) in bills over his head for his part in the challenge.
A video posted online shows Sheen, who was nominated by hockey player Ryan Miller, tipping a silver bucket full of money over his head and exclaiming: "Oh wait, that’s not ice. That’s $10,000 in cash which I am donating to the ALS Foundation because let’s face it, ice is gonna melt and this money is actually going to help people (sic)."
Sheen nominated his former Two and a Half Men co-star Jon Cryer, the show’s creator Chuck Lorre, and replacement cast member Ashton Kutcher.
"I am hereby calling out Jon Cryer, Chuck Lorre and Ashton Kutcher to identically do what I just did. C’mon guys, it’s for a great cause,” he said.
Facebook founder Mark Zuckerberg has done it and wants Bill Gates to do the same.
Zuckerberg, who was nominated for the challenge by New Jersey Governor Chris Christie, laughed as he tipped the ice over himself before daring Microsoft titan Bill Gates to do the same.
He also challenged Facebook executive Sheryl Sandberg and Netflix director Reed Hastings to follow suit.
“You guys have 24 hours to complete the challenge or you have to donate to the ALS foundation - or both,” he said.
Television star Jimmy Fallon, singer Justin Timberlake and actor Mickey Rourke, along with several sports stars have all taken the challenge in recent weeks.
Even the 86-year-old widow of Robert Kennedy, Ethel Kennedy, has taken the challenge - urging President Barack Obama to do so. Obama declined, but made a donation.