Kohl, the best climber at this year's race where he finished third overall, has become the fourth rider to test positive for CERA, a new generation of the banned blood booster EPO (erythropoietin).
In all seven riders tested positive at this year's race, which was won by Spaniard Carlos Sastre of the CSC team.
Italians Riccardo Ricco and Leonardo Piepoli and
Ricco followed Spanish duo Manuel Beltran, of Liquigas, and Barloworld rider Moises Duenas in leaving the race, both of whom tested positive for EPO.
On the race's final day it was revealed that Dmitri Fofonov, a Kazakh who rides for Credit Agricole, tested positive for a banned stimulant. He has since been banned for three months.
Weeks ago it was confirmed that Ricco's teammate Piepoli, a climber who won the 10th stage to Hautacam in the
Then last week Schumacher - Kohl's team and room-mate at Gerolsteiner - was also confirmed as having tested positive for CERA. The German won both time trials on the race.
On Monday Kohl was the latest rider to be snared for using EPO to oxygenate his blood cells, thus boosting his abilities to perform on the world's toughest bike race.
Although it had been reported recently that
The French anti-doping agency (AFLD) was in charge of this year's controls as the Tour was being held outwith the auspices of the International Cycling Union (UCI) because of a dispute, which has now been resolved. The AFLD recently pioneered a new blood test for CERA, the latest generation of a drug which has been in use in endurance sports since the early 1990s.
(c) AFP 2008