All aboard for Samba! Chaotic, noisy, sweaty fun--that's National Samba Day on the train to Oswaldo Cruz.

If you play cavaquinho, a type of plucked lute for samba music, and write songs for one of the best-known samba schools in Brazil, every day is a day worth celebrating.

But National Samba Day in early December is something special, says cavaquinho musician Flavio Oliveira, looking out from behind the stage at Rios Central Station at thousands of people preparing to board the annual samba trains.

The trains depart for Oswaldo Cruz, the neighborhood that was home to many of samba's pioneers during the 1920s. Then, samba was not considered a respectable pastime and its early artists were forbidden from playing in the city. One of the few places they could meet and jam was on the last train home from work.

A few years ago, aficionados invited samba bands on National Samba Day to play on the trains heading for Oswaldo Cruz, one in each car. The tradition has grown and on Dec. 2 fans of Brazil's national sound climb aboard among bemused and besuited commuters, old samba hands in rakish Panama hats, and bohemian youngsters with drums, cavaquinhos and tambourines. They all squeeze onto the crowded evening trains heading towards the suburbs.

"There is nothing that sums up Brazil better than samba," Oliveira says as he prepared to board the train with the other members of Salgueiro's Old Guard, the samba school's venerated elderly wing. "It is the essence of the Brazilian people and this date is very important. The samba train is the perfect compliment to the day's celebrations."

Typically for Rio, the party was chaotic and, just as typically, the locals reveled in the chaos. When the third train pulled out of the station just after eight o'clock, people banged empty beer cans together and slapped out the beat on the windows and walls to the unmistakable rhythm of the drums. The crush was such that there was barely room to stand up, never mind dance.

Fittingly, the first samba was Tropical Geography, a song composed by passengers on the original samba train to celebrate the stops along the line. When the train reached Mangueira, home of the current carnival champions, the train rocked to the sounds of old Mangueira standards. When it passed through Madureira, the last station before the end of the line, the cars resounded to the singing of The Time Has Come.

The train shuddered to a halt in Oswaldo Cruz just before 9 p.m. and a mass of humanity poured onto the platform, the steamy air thick with smoke from the dozens of barbecues, exhaust fumes from huge traffic jams and mellifluous sound of hundreds of people singing yet one more samba. "Look at this, this so democratic," says samba train rider Ana Cristina Albuquerque, an architect. "There's rich and poor, black and white. If you like samba, this is the place to be."

There's plenty of reason to celebrate. In a more that mirrors that of their fellow pensioners in Cuba's Buena Vista Social Club, documented in the 1999 film of the same name about aging Cuban son players, the older members of samba schools are recording their music for the first time. Some have gone to Europe on tour. One old sambista, Martinho da Vila, recently recorded an album of sambas in French, and another, Paulinho da Viola, was the subject of a successful biographical film.

Heart and soul. Commercially, samba is also getting its act together. Four of the top 10 artists in Brazil's three main markets are samba artists, more than any other genre. The schools that form the backbone of the US$140 million carnival season are setting up joint ventures with Brazilian and multinational companies that can bring them as much as hall a million dollars in sponsorships each year. Even the Rio city government is getting in on the act, recently announcing it will spend $25 million to build Samba City, a musical theme park with shops, restaurants and concerts.

But the heart and soul of the music and its rebirth lies in events like a ride on the samba train. Once in Oswaldo Cruz, many stayed to listen to the masters play on a big stage and many more hung out at one of the dozens of little bars where the impromptu jam sessions were getting under way.

Some trains headed straight back to the city center but few boarded them. Everyone wanted to stick around and hear just one more.