The Federal Court in Lausanne has ruled that the International Cycling Union must provide the Italian justice authorities with the names of 15 riders tested for drugs during last year's Giro d'Italia.
The Federal Court overturned an appeal by the Lausanne-based body against handing over the documents.
The ICU carried out the tests in June 1999 before the start of the Pedrazzo to Madonna di Campiglio stage of the race. Thirteen of the 15 tests reportedly showed traces of the banned substance EPO.
In its judgement issued on Tuesday, the Federal Court rejected the ICU's argument that the Italian authorities did not need the information for their own enquiry and that providing it would constitute a breach of confidentiality.
The court ruled that the Italian investigators were entitled to know the identity of the riders concerned. It said they were investigating whether the suspects were involved in trafficking the drug, and were not concerned with whether they had broken the rules of the sport.
The ruling comes a day after the International Olympic Committee, also based in Lausanne, approved a blood-urine test for detecting EPO. The IOC plans to test competitors for the performance-enhancing drug before the start of the Sydney Olympics next month.
swissinfo with agencies
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