Helmeted or bare-headed -- and often wearing nothing else at all -- some 30 cyclists braved the rain in Sao Paulo, Latin America's largest metropolis, to sensitize motorists to their "vulnerability" on the road.
Most riders on Paulista Avenue, one of the busiest arteries in Brazil's economic capital, were in fact nude. Some, a bit more modestly, preferred wearing minimal underwear.
One rider wore a Russian-style chapka on his head and nothing else but the green paint that covered him from head to toe.
The group was taking part in what is called the Pedalada Pelada (Pedaling Bare), the Brazilian version of the World Naked Bike Ride movement.
"We are naked on one of Latin America's biggest avenues, showing that we are vulnerable to the force, the violence of cars," Allis Bezerra, a bearded 41-year-old photographer, told AFP.
He added: "This movement serves to demonstrate to society just how important we are. By using bikes as our means of transport, we take cars off the street that would be polluting the environment."
Andresa Aguida, a 43-year-old artist, had the message "Sustainable Pedaling" painted on her stomach before setting off, bare-breasted, on Paulista Avenue.
"Motorists show us no respect when we are riding," she said. "They honk and seem to be saying: 'Move or I'll run you down.'"
Cyclists were hospitalized in more than 16,000 serious accidents in 2021 -- an average of 44 a day -- according to a study published last June by the Brazilian Association of Traffic Medicine, or Abramet.
Pedalada Pelada is planning its next clothing-optional demonstration next Saturday, this time on the streets of Rio de Janeiro.