BARCELONA, Spain — Each year since 2004, Jacint Ribas has taken out his bicycle in March, and wearing nothing more than his salt-and-pepper hair, has pedaled it through the streets of this port city. By now he reckons he has covered about 4,800 miles, opening the season for going undressed in public.

One year he was stopped by the police 30 times, and released again each time because he was not breaking the law. “I do it to show that it’s normal,” said Mr. Ribas, 62, a retired bank employee who is president of the Association for the Defense of the Right to Nudity, as he sipped wine and munched ham slices.

The annual exercise began in 2004 because that was the year that the Barcelona City Council subsidized a brochure with the intriguing title, “Expressing Yourself in Nudity.” Illustrated with photos of ordinary citizens naked on the street, in the subway and in the city’s parks, it affirmed categorically that the law “does not contain any article for sanctions against public nudity.”

It went on to say that the city respected “the right of the citizenry to nudism,” and boasted that one year earlier, in 2003, no fewer than 7,000 people volunteered to undress together in Barcelona.