More than 150 naked cyclists coursed their way through inner-city Melbourne in support of bike activism on Sunday.

Melbourne's fourth annual Naked Bike Ride kicked off at the Edinburgh Gardens in North Fitzroy and took riders on a 10-kilometre trip through the city's streets.

Organiser Heidi Hill says the ride protests in favour of bike activism, as well as naturism, environmentalism and pacifism.

She says it a sure-fire way of bringing attention to those issues.

"Going past Lygon Street and all the restaurants, people come running out and they're quite shocked and then they start laughing and screaming," she said.

"I think people are titillated and excited to see people having so much fun."

She says riders wore little more than body paint slogans.

"Slogans are fantastic this year. They're quite political," she said.

"There's some to do with the Libyan situation. There is Berlusconi this year. Mostly it's about freedom and about bike activism, like 'please cycle safely', and 'bike love'."

abc.net.au