Former Olympic gold medal winner Tim Montgomery pleaded guilty to federal heroin distribution charges on Thursday.

Montgomery, who won gold in the 4 x 100-metres relay in Sydney in 2000, appeared briefly before US District Judge Jerome B Friedman, who asked the former 100-metre world-record holder if he understood the guilty plea.

Montgomery, who was charged with conspiracy to possess with intent to distribute and distribution of over 100 grams of heroin, politely responded with answers of "Yes, sir" and "No, sir" to Friedman.

Already serving a four-year prison sentence for his role in a cheque-fraud conspiracy, Montgomery faces a minimum of five years in prison when he receives his sentence on the heroin charges, scheduled for October 10.

Montgomery also could be fined up to US dollars 2 million and faces at least four years of supervised release.

According to the Drug Enforcement Administration (DEA), Montgomery sold 111 grams of heroin for nearly US dollars 8,500 to an undercover DEA informant. Four meetings between Montgomery and the informant were videotaped and recorded by the DEA. 

Despite being led into Norfolk's US District Courthouse in handcuffs, Montgomery was smiling and laughing with defence attorney James O Broccoletti.

But there is very little for Montgomery, 33, to smile about these days. He pleaded guilty in federal court in Manhattan in April 2007 to conspiracy to commit bank fraud and two counts of bank fraud in a counterfeit cheque scheme that also embroiled fellow Olympic champion sprinter and former partner Marion Jones.

Thirteen months later, Montgomery received a jail sentence of three years and 10 months for his role in the scheme.

Montgomery retired from track and field in December 2005 in the wake of receiving a two-year doping ban, not for failing a drugs test but on the basis of an admission he gave about his use of steroids in 2001 in testimony to the 2003 BALCO investigation.

His ban from the sport also brought with it an order to return his Olympic medals, the gold he won in Sydney and a silver in the same event at the 1996 Atlanta Games.

Montgomery's world record-breaking 100 metre run of 9.78 seconds, set in Paris in 2002, also was erased from the historical lists.