Cyclist Floyd Landis gives an exclusive tour through what he and others say is a culture of systematic doping in the sport.

Nine days into the 2004 Tour de France, the U.S. Postal Service cycling team, led by Lance Armstrong, checked into a hotel near the village of Saint-Léonard-de-Noblat.

It was July 12, one of two rest days on the Tour—the rare breaks that give riders a chance to rest and gird themselves for the punishing climbs and sprints that make this the most depleting event in professional cycling.

According to one of the U.S. Postal team's most prominent riders at the time, Floyd Landis, one room at the hotel had been set aside for a secret procedure.

Outside its door, Mr. Landis said, team staff members were stationed at each end of the hall to make sure nobody showed up unannounced. The riders were told before they went into the room not to talk when they got inside, he said. The smoke detectors had been taken down, he said, plastic was taped over the heater and the air-conditioning unit, and anything with a hole in it was taped over. The purpose, Mr. Landis figured, was to obscure the view of any hidden camera.

The riders on the team who participated in this procedure lay down on the bed, two at a time, Mr. Landis said, with a doctor on each side. Mr. Landis said he got a blood transfusion. He said he also saw Mr. Armstrong and two other team members, George Hincapie and José Luis Rubiera, taking blood. He said he didn't see any other riders getting transfusions that day.

The procedure, which enhances performance by boosting a rider's red-blood-cell counts, is considered cheating by the International Cycling Union, the sport's governing body.

Mr. Landis said that he isn't sure what happened to the empty blood bags, but that on other occasions he had seen team staffers dispose of them by cutting them into tiny pieces and flushing them down the toilet.

Doping is a scourge in professional athletics, and pro cycling has seen numerous scandals and suspensions over the past decade. The picture painted by Mr. Landis in the interviews, and in a series of emails he wrote to cycling sponsors in May, provides the most detailed view yet of what may be one of the biggest and most intricately coordinated cheating conspiracies in sports history. It involves blood transfusions taken in a bus on a remote alpine road, riders wearing testosterone patches to bed, and an operative posing as an autograph-seeking fan to deliver a bag of blood to a rider after a race.