Kate McCann, mother of missing Madeleine, hopes to raise £10,000 for charity as she sets off on an Edinburgh to London bike ride.
Mrs McCann will join around 20 cyclists for the five-day, 500-mile challenge in aid of the UK charity Missing People.
Due to set off from the centre of Edinburgh today, they will take in Newcastle, York, Nottingham and Northampton before crossing the finish line in London on June 17.
Mrs McCann is an ambassador for Missing People and last year launched Child Rescue Alert, which has seen more than 250,000 people sign up to receive alerts when a child is feared to have been abducted.
She said: "The Missing People Cycle Challenge is particularly significant for me, a year on from the launch of Child Rescue Alert in the UK.
"The night that our little girl was taken from her bed, we mistakenly presumed that an alert would have gone out immediately to the public to get as many eyes and ears involved in the search as possible.
"But no such system existed to get a message out into the public domain quickly and recruit help. Although a simple idea, Child Rescue Alert is a potentially life-saving system, the success of which is reliant on us, as members of the public, to sign up to receive free alerts when a child goes missing.
"I hope that with every push of a pedal the Missing People cycle team makes from one end of the country to the other, we will encourage more and more people to join us in support of the charity and in solidarity with all of those families waiting at home, in limbo, without news of their loved one."
Missing People chief executive Jo Youle said: "Every year I am deeply moved by the way the Cycle Challenge brings together families desperately missing loved ones with supporters of the charity, all pulling together in solidarity so we can offer a lifeline when someone disappears.
"As the team members stretch themselves and support each other with every aspect of the Challenge, they always keep in mind the many missing adults, children and families that the charity supports."
To donate to Kate McCann's Cycle Challenge visit www.justgiving.com/KateMcCann
To sign up to receive free Child Rescue Alerts, visit www.childrescuealert.org.uk/register