Four friends will aim to play four rounds of golf in a single day to raise £4,000 for Macmillan Cancer Support.
Sheffield golfers Steve Manley, James Wells, Oliver Hague and Wayne Bishop will play 72-holes, walk 20-miles and hit around 300 shots during their mammoth dawn until dusk challenge.
The quartet plan to tee off at 4.30am on Friday, June 28, at Hillsborough Golf Club.
As well as raising money for Macmillan Cancer Support, the men are hoping for the chance to head to Portugal to play for the Longest Day trophy in October.
Two years ago, Steve led a team which made it through to the finals in Portugal, the first from Sheffield do so.
Steve said: “To know that by taking part we will be helping Macmillan to continue the fabulous work they do to support people affected by cancer will drive us on.
“We had two teams entered last time, the day started at 4am and ended at 9pm but we all played the last hole together.
“The eight of us walked down the final fairway to a packed clubhouse who were all cheering us on. It was a fantastic and unforgettable experience that we hope to repeat this year.”
Macmillan fundraising manager for Sheffield, Rob Turner, said: “We are very grateful to all the team for taking on this golfing challenge.
“I know they are determined to raise a huge amount of money for us and I wish them the best of luck.
“The money raised from this challenge will help Macmillan support people affected by cancer in Sheffield.”
In 2012, over 500 teams took part in the challenge and raised more than £565,000.
Visit www.macmillan.org.uk/longestday for more information.