In 1998 the Brazilian director Walter Salles made one of the most powerful films of the past decade: "Central Station." Now "The Motorcycle Diaries," his new film, is the story, told from the diaries and letters of his protagonists, of the year - 1952 - that Ernesto Che Guevara, then a 23-year-old medical student in Buenos Aires, and his friend Alberto Granado, a 29-year-old graduate student in chemistry, decided to go on a trip by motorcycle the length of South America. They start out on Alberto's old 1938 Norton 500 machine, a pathetic thing that leaks oil and is greatly overloaded, planning to stop first at the ranch of Che's girlfriend Chichina (Mia Maestro) and then head for the Andes, the Amazon basin and the Caribbean.

It's a lark, and Che (Gael Garcia Bernal) and Alberto (Rodrigo de la Serna) are having a ball. After leaving Chichina behind they use their wit and charm to get free lodging, food, drinks and even motorcycle repairs, while romancing the local wives along the way. Sometimes it works, sometimes they're chased out of town by angry husbands.

But Salles isn't content with a comic version of "Easy Rider." Che has asthma attacks that can only be treated with quick injections of adrenaline. When they reach the Andes they're confronted by the sight of the worst kinds of corporate colonialism: they meet peasants who've been forced off their lands by (often) foreign companies, in collusion with their own governments. The peasants starve, or are forced to work in dangerous mines (Anaconda is a villain here). They visit Machu Picchu and Che studies the great achievements of the indigenous Indians. Salles is preparing us, of course, for Che's epiphanies that will turn him to an uncompromising revolutionary in the few years remaining to him.

And so the second half of the film becomes an encomium to the young revolutionary-to-be. Che and Alberto sign on as medical volunteers at a hospital for lepers in the Amazon basin, and in the weeks they spend there, they perform near-miracles of at least emotional healing of the depressed patients, and even convert the Catholic mother superior who runs the hospital into a more modern, relaxed administrator. And then, to top it off, Che swims the broad river from the hospital side to the residence side, so that he can say farewell to his patients. The asthma attack he suffers in mid-river is just a little extra that Salles throws in.