Officials of those labs also suggested that some athletes may have taken those substances unknowingly because they were improperly labeled.

"We strongly advise governmental authorities to take measures to prohibit the sale, manufacture and importation of unlicensed preparations of nutritional supplements contained prohibited substances, whether labeled or not," the 27 labs accredited by the International Olympic committee said in a statement.

Officials have been puzzled by the sudden surge in positive tests for nandrolone, which has been available for decades and is easily detectable in standard urine controls. Many believe the increase is the result of athletes' taking supplements which, they may or may not know, contain nandrolone.

Former world champion sprinter Merlene Ottey and former Olympic champions Linford Christie and Dieter Baumann have been among the stars who have been suspended recently after testing positive for the drug. All have protested they are innocent

The heads of the 27 labs accredited by the International Olympic Committee said they had considered new data on nandrolone as well as looking at mislabeled nutritional supplements, at a meeting in Germany.

They said the new studies "reconfirm the validity of the current reporting criteria used by IOC-accredited laboratories."

The International Amateur Athletic Federation agreed earlier this month to study the possible effect of food supplements on those who failed the nandrolone tests. But pending the results, it is retaining its penalties for athletes testing positive for the banned steroid.