Chart star Jessie J will tonight pull off a hair-erasing feat as she shaves her head on live TV, while many of the biggest names in comedy do their bit for the UK's Comic Relief.
Miranda Hart, Dawn French, James Corden, David Walliams and Hollywood star Will Ferrell will appear in sketches or in person during the evening in the traditional Red Nose Day broadcast on BBC1 and BBC2.
Price Tag singer Jessie will be enduring one of the biggest sacrifices as she is parted from her glossy black bob during the programme to boost the millions of pounds being raised.
Red Nose Day celebrates its 25th anniversary this year, with presenters tonight including Rob Brydon, John Bishop, Davina McCall, Nick Grimshaw, Jonathan Ross and Russell Brand.
During the evening, Hart will round off her week of live TV challenges, Miranda's Mad March, in addition to starring in a special edition of Call The Midwife, alongside Jessica Raine, Pam Ferris and Jenny Agutter.
Popular sitcom The Vicar Of Dibley will return to TV for the first time in seven years with a one-off sketch, created by Comic Relief boss Richard Curtis.
Corden will be reviving his role as Smithy from Gavin And Stacey, and Ferrell is to return to his character Ron Burgundy from hit movie Anchorman.
X Factor's Simon Cowell will show his lighter side by taking part in a spoof in which he walks down the aisle alongside David Walliams dressed as a blushing bride.
Other highlights will include:
• The return of David Brent as Ricky Gervais for a brief revival of The Office, in which he shows off his new career as a wannabe music mogul.
• Rowan Atkinson will address as the new Archbishop of Canterbury, sharing his views on the importance of fundraising for Red Nose In Need.
• Peter Kay will be seen undertaking his challenge to spend much of the week perched on a sofa, as well as unveiling his new video for the James hit Sit Down.