Some 3,000 demonstrators -- some bare head to toe, others in bathing suits or underwear -- braved catcalls and embarrassed smiles from residents as they biked some 12 miles (20 kilometers) to end up in Guadalajara, the biggest city in Mexico's Jalisco state.
In downtown Mexico City, nearly 2,000 bikers -- naked or scantily clad -- also demonstrated. Some slapped "fragile" stickers on their bodies or painted messages on their skin: "more bicycles, less pollution," and "the city is for everyone, let bikes pass."
By stripping bare for the ride, the cyclists aimed to highlight the fragility of riders, and the risks they face, on busy roads.
But for the protesters in Guadalajara, it was also a chance to take a swipe at the conservative climate in that state.
"It's a very conservative city, and I believe that daring to (cycle naked) pushes beyond the limits of the Catholic sense of morality," said bathing suit-clad Lucia Escalante, participating in the rally for the first time.
"That's why it's more important to show here that we are free," the 27-year-old added.
Jalisco, the home of tequila and mariachi music, has in recent years hosted a number of similarly provocative events, including Mexico's biggest gay pride parade.