Steven Spielberg, Justin Bieber and Bill Gates are among many celebrities pouring buckets of ice water over their heads and donating to fight Lou Gehrig's disease, in a fundraising effort that has gone viral.
Since June, several thousand people worldwide have recorded themselves getting drenched, then posted the stunt online and challenged others to do the same, or pledge $100 to ALS research.
Many have done both, in an effort has raise millions of dollars for the ALS Association, which combats amyotrophic lateral sclerosis, also known as Lou Gehrig's disease.
Some 30,000 Americans have ALS, which attacks the nervous system and eventually leaves victims paralyzed.
In just weeks the "ALS Ice Bucket Challenge" has swelled into a global phenomenon, with dozens of stars getting wet: Lady Gaga, Britney Spears, Justin Timberlake, Taylor Swift, James Franco, Oprah Winfrey, Jennifer Lopez and Jon Bon Jovi are among them.
Politicians and sports figures went at it too, including New Jersey Governor Chris Christie and basketball superstar LeBron James.
Bare-chested English footballer David Beckham got in on the act, as did World Cup stars Neymar of Brazil and Argentina's Lionel Messi.
Normally reserved former US Federal Reserve chairman Alan Greenspan can be seen gleefully dumping ice water over his wife, MSNBC anchor Andrea Mitchell.
Microsoft founder Bill Gates, recorded himself taking icewater to the head, responding to a challenge by Facebook's Mark Zuckerberg.
Ethel Kennedy, the 86-year-old widow of senator Robert Kennedy, doused herself and challenged President Barack Obama to do the same. The world's most powerful man declined but promised a donation, according to the White House.
The charitable challenge's popularity has spread around the globe in recent days, particularly to Britain, Australia, New Zealand, Canada and Germany.
Facebook said that between June 1 and August 17 more than 28 million people mentioned the challenge on the social network, and 2.4 million videos were posted.
The phenomenon can largely be attributed to Pete Frates, a one-time athlete in Boston whose struggle with ALS turned the Ice Bucket Challenge into a viral fundraising sensation.
A flood of funds—$22.9 million from July 29 to August 19, compared with $1.9 million for the same period in 2013—has poured into the ALS Association, which welcomed "the incredible influx of support."
"We need to be strategic in our decision-making as to how the funds will be spent so that when people look back on this event in 10 and 20 years, the Ice Bucket Challenge will be seen as a real game-changer for ALS," said association president Barbara Newhouse.
About 5,600 new ALS cases are diagnosed each year in the United States.
The Internet has helped raise support for such causes, notably allowing organizations combatting lesser-known illnesses to raise much-needed money.
Some experts argue that such groundswell movements are narcissistic and give digital activism a bad name.
"The Ice Bucket Challenge went viral because of the potent mix of celebrity, simplicity, and comedy," warned sociologist Jen Schradie, a doctoral candidate at University of California, Berkeley.
"I doubt most people participating even know what ALS is, and that is the problem with this form of clicktivism: it does not promote a deep understanding or a long-term relationship with a cause."