Hundreds of walkers highlighted the plight of those who suffer from Crohn's disease in a sponsored event.
Duncan from boy band Blue took part in last year's walk
Walk for Crohn's was organised by north-west Londoner's Natasha Adley, 18, and Lisa Meleck, 19, whose mothers have the illness.
Crohn's disease is a long-term illness that causes inflammation in the gut. Current treatments often require hospitalisation and surgery.
Last year the event in Hyde Park raised £32,000 for two Crohn's charities.
Natasha, from Stanford, and Lisa, from Northwood, came up with the idea for the event about two-and-a-half years ago.
The disease can be very painful as well as causing severe diarrhoea. The cause of the illness itself is unknown.
Natasha said: "It's all about raising awareness as well as raising money. It's a big step forward to get people involved so whatever we raise is good."
The girls managed to get more than 300 walkers involved last year and footballer Les Ferdinand and Duncan James from Boy band Blue also took part.
This year singer Louise Rednapp will be launching Sunday's event and Ferdinand is offering his support for a second year.
All money raised is split between the Kati Jacobs Appeal, which is helping to build a centre for research at St Mark's Hospital in Harrow, and the Crohn's and Colitis in Childhood charity.