The 28th Annual BP MS 150 is the largest event of its kind and the largest fundraising ride for the National Multiple Sclerosis Society.
About 13,000 cyclists of all ages are pedaling the 182 miles from Houston to Austin.
Participants started the two-day trip Saturday from three different locations in the Houston area -- Tully Stadium in west Houston, Rhodes Stadium in Katy and Waller Stadium in Waller County.
The riders will camp out in La Grange overnight before heading to Austin on Sunday.
The BP MS 150 ride aims to raise $17 million this year to fund cutting-edge research and support programs and services benefiting 56,000 Texans affected by MS.