While US track and field has been enjoying the unprecedented success of the Sacramento Olympic trials, which have produced record crowds and encouraging television ratings, the sport looked to be mired in controversy yet again as the former director of the US Olympic Committee's drug control programme, Dr Wade Exum, filed a lawsuit on Monday alleging that US athletes who have tested positive for drugs have escaped punishment and disclosure and have gone on to win medals at the Olympic Games.

Exum, who spoke in Ireland at a drugs conference two years ago, also alleges that the US Olympic committee has declined to impose any penalties on approximately half of the American athletes who have tested positive in recent years.

Exum, who is suing the USOC for wrongful dismissal, feels his opportunities within the organisation were limited because of his race (he is African American) and because of the scrupulousness with which he performed his duties. His lawsuit, filed in Denver, Colorado, does not name specific athletes or cases.

US Olympic officials declined to comment on the case in detail but USOC president Norm Blake released a statement to the effect that the their "cursory review suggests that the complaint is without merit and statements previously made by Exum are without merit".

Brazil's 400 metres world silver medallist Sanderlei Parrela, who has been suspended by his federation after testing positive for nandrolone, denied the charges yesterday. The runner, who can no longer participate in the Sydney Olympics, claimed that any substances he has taken have been severely controlled by doctors.