Kidney patient Tim Manhire plans to travel almost 1,500 miles by motorbike to raise cash for the charities which have helped keep him alive.
The Customs officer hopes the gruelling trip will raise £3,000 for the National Kidney Research Fund and South-East Kidney Patient Association.
The charity ride, to Britain's most easterly, northerly, westerly and southerly renal units, is expected to take four days.
Tim, of Milton Road, Crawley, has suffered from kidney problems since he was seven.
He set off on his Fazer 1000 Yamaha yesterday from the Royal Sussex County Hospital, Brighton.
Tim, 50, said: "I'm hoping to make Norwich today, then up to Inverness. After that I go to Bangor in Wales before heading back here."
He said the only thing which could slow him down was his left arm because it was weaker as a result of an operation preparing him for dialysis.
He said: "The operation knocks some blood out of your arm so my left is actually colder and not as strong.
"Hopefully I won't get too many traffic jams because the clutch lever is on that side."
An experienced long-distance biker, Tim has already completed a trip across America, from New York to Los Angeles.
Tim's friends, family and work colleagues have sponsored him for the ride. American Airlines has also donated two tickets to the United States for Tim to auction.
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