"Be on the boat early," the guidebook said, "to reserve a hammock space." It wasn't specific about how early to stake a claim on the top floor of an Amazon passenger boat.

It also didn't point out that a lot of the locals would get there two days early.

The Amazon is still the major line of communication across Brazil: What roads there are are frequently impassable, and can reduce a bus to a collection of spare parts in just a few trips. The river is fed by more than a thousand tributaries, making it the largest in the world in terms of water volume. The Amazon basin, which covers more than 2.3 million miles and teems with jungle plants and wildlife, is one of the most exotic regions on Earth.

For the traveler, then, a trip up the Amazon is a must. But there is a world of difference between school-day dreams in a geography classroom and actually making the voyage.

Most people making the 1,200-mile river journey from Bele'm to Manaus use the government's ENASA line, which runs diesel passenger boats several times a month, with accommodations ranging from luxury to third-class. But if you don't want to wait, there is an alternative.

Smaller, two-decked wooden boats also ply the river. These boats are usually about 200 feet long; their lower decks are half-filled with cargo, then topped off with passengers. As the boats suffer from engine noise and fumes -- and, at least on our boat, the smell of the cargo of onions -- the fares are often slightly cheaper than the government line's. These small boats, however, do not go all the way to Manaus; passengers must change boats midway through the journey, at the city of Santare'm.

It's impossible to predict how many passengers will be on board. In our case, a gold rush in the Itaituba area caused a surge in passengers heading up the Amazon as far as Santare'm; 350 people were crowded on the two decks of the Fe' em Deus (Faith in God), a small boat designed to hold 200.

There was no question of reserving a space. Late arrivals strung their hammocks over, under or across those of others, using every bit of space. As the boat continued to fill up two hours after the scheduled departure time, passengers lay in their hammocks glaring malevolently as newcomers tried to squeeze into smaller and smaller gaps.

My friend and I were lucky -- we managed to position our two hammocks side by side, with only one hammock strung diagonally above us.

As the boat slipped its moorings and headed out into the night, the buzz of conversation quieted down. The boat drove through the night, yards from the dense wall of the Amazon jungle.

"Crowded" took on new meaning as we surveyed the passenger area. The route to the restrooms was all but barred by hammocks weighed down with sleeping bodies (the easiest way to get there, we soon found, was to drop on all fours and crawl). Passengers were even strung up over the dining table. There they slept, while below them miners playing cards sat hunched by the one electric light that shone all night.

We settled in to sleep as best we could. In the hammock next to me (we bumped regularly through the night) was a rather stout woman with a solemn little child who was constantly pampered, dressed and fussed over. During our three days together, we passengers were to become all too familiar with one another's personal habits.

At about 5 o'clock the next morning, the darkness was split by a handbell being rung and a hoarse voice bellowing: "Cafe', cafe'." Breakfast was ready. It consisted of weak Brazilian coffee laced with sugar, served with a side dish of very stale biscuits. We queued up, unshaven and unwashed, and sat down in shifts to drink our breakfast.

Three hundred fifty passengers were a real strain on the Fe' em Deus' 12-man crew and the limited cooking facilities on board. Chicken, rice and beans were served for every lunch. Supper was slightly more erratic. The first supper of rice was enlivened by small cubes of beef; there was a lot left over, and it reappeared in the beans of the next day. By the time it resurfaced in a soup the day after, even the locals complained.

Naturally enough, considering our predawn breakfasts, lunch and supper were served early: The first sitting for lunch was served with little ceremony at about 10:30 a.m. The locals washed their meals down with glasses of murky brown Amazon water.

The first day's journey was spent negotiating the narrows, a maze of little waterways that thread through virgin jungle in a navigator's nightmare. As the banks widened out signs of settlement appeared, and small boys in dugout canoes paddled out, shouting. Sometimes the passengers threw gifts, ranging from empty water bottles to wadded-up bank notes. Some children paddled through the wake of the boat to retrieve their gifts. Others, more dignified, waved solemnly from the bank as we chugged past.

The jungle, tangling to the bank, seemed impenetrable. On the water's edge, we spied several creatures that we soon christened "logodiles" (i.e., logs that look rather like crocodiles) and an occasional heron. We also saw flocks of parrots in the trees -- but in general, I'd seen more wildlife in Bele'm market.

Perched over the guard rail, a lackadaisical Canadian swung in his hammock, ironically quoting his guidebook: "The patient watcher will see plenty of wildlife." A passer-by accidentally bumped his hammock, and he swung wildly over the water. "Many travelers find the trip worthwhile," he quoted again.

Even so, it was nice to be able to see the bank. Going upstream, the boat stuck close to the edge, avoiding the current. Downstream, it sailed in the middle of the river, using the current, and the bank was a distant line on the horizon.

As we moved along, we stopped at various small settlements, sometimes during the day, more often unobtrusively, in the middle of the night. A plank would be slung across to the bank, and porters would gingerly walk across with sacks and boxes.

As we entered our second day on the river, the boat began to show signs of strain. The once-clean floor was littered with bottles, glasses and rubbish. The piles of luggage and the canopy of hammocks made cleaning up impossible. The passengers, however, kept themselves very clean, queuing up for two or three showers of river water every day.

Our routine on the boat was tied closely to the rhythm of the sun. The predawn breakfast ensured our early rising. And as soon as it got dark, the few lights on board were turned off, as they tended to attract jungle-sized flying insects. In the gentle warmth of the night, the subdued throb of the engine soon lulled us to sleep.

We arrived at Santare'm after breakfast on the third day out. Here we were to transfer to another riverboat.

In Santare'm, the green waters of the Tapajo's flow alongside the yellow waters of the Amazon proper. This meeting of the waters can be clearly seen from the boat, and later from the bank, and rivals the more publicized meeting of the waters up by Manaus.

Santare'm is a quiet backwater town with a fascinating waterfront market where all kinds of boats meet and trade. Any thoughts of going to Itaituba to see the mine fields were instantly abandoned when we saw the boats: If our boat had been crowded, these were even worse. More than 400 people were stacked in their hammocks with no room to stand. They did not appear to be looking forward to their six-day trip to Itaituba.

By contrast, our new digs were palatial. The owner's wife, a stout, middle-aged woman in tight purple shorts, swept and polished the wooden floor until it gleamed, segregated men and women onto the two sides of the deck (unless married), and confiscated playing cards as soon as she saw them. She was a bit domineering, but she ran her husband's ship smoothly, efficiently and hygienically. For $20, including all meals, we traveled first class to Manaus; this meant that we were able to sling our hammocks along the uncrowded upper deck, and wander around in spaces not dominated by hammocks full of people. Most of the Brazilians preferred to save $2 and travel downstairs, sharing their space with piled-up cargo and the fumes from the engine.

We had all our old friends from the previous boat with us: the group of young Brazilian bachelors coming to buy electronic equipment in duty-free Manaus to sell in other parts of the country; the young French pilot in his third year of traveling; another Frenchman finishing a two-week tour of South America and planning to "do" Africa the next month. We lay around in each other's hammocks and swapped stories, drinking purified water and an occasional beer.

Our new boat was more comfortable, but it didn't work as well as the last. We hadn't gone far before the engine lost power and gained smoke, and we drove into the bank. With apparent disregard for the risks of piranhas, electric eels or any of the other unpleasant fish that lurk around in the depths, someone dived off the side and swam to attach a rope to a tree.

After the initial excitement, most of the passengers relaxed in their hammocks and settled in for a wait, to the tune of muffled curses and dropped spanners from the engine room. Then the man on the shore found a hornets' nest.

Unfortunately, the nest was well out of his reach, and his efforts to dislodge it with a stick only had the effect of annoying the hornets. Gradually they thickened into an angry, buzzing surface on the nest. It was in the nick of time that the boat restarted, and we moved on at half-speed.

We continued up the river, hammocks swaying gently through the heat of the afternoon.

It was my traveling companion's birthday, and as Brazilians don't need much encouragement for a party, this was enough.

At the next stop one of our new friends slipped off the boat and, careful not to alert the captain, came back with a few bottles of cachasa, the local firewater.

Bottled by the same factories that produce the alcohol that most cars use as fuel in Brazil, cachasa is very cheap and very strong. Mixed with sugar and lime, it is almost drinkable.

Soon the front of the boat was transformed, with birthday greetings written on lavatory paper strung up as bunting, and impromptu singing and dancing.

Various crew members passed by and looked around curiously: We were trying to be discreet, but the front deck was beginning to smell like a Brazilian gas station, and soon the party was in its prime.

At the next port, a search party was sent out for more cachasa, but it was intercepted by the captain. Probably just as well -- there were headaches at supper.

On this boat, supper consisted of chicken, beans and rice. So did lunch. Every day. At least we weren't served stale biscuits with breakfast; they just gave us coffee.

Because of the problems with the engine, it took three full days to get to Manaus. We knew we were getting close when the land became more open, with domesticated water buffalo and cattle grazing in bright-green tropical grass.

We saw logging skid-paths on the banks, then the occasional factory, and finally the city itself. Wooden houses were built high on stilts above the water level, which had risen to flood large tracts of land.

Passenger boats were stacked several-deep against the bank, and we clambered with our luggage along precarious planks to solid land. We had covered more than 1,200 miles on the greatest river in the world. Jack Barker is a free-lance writer living in London.