Montgomery and Gaines receive two-year bans
The CAS announced their decisions on the pair, who had been charged by the US Anti-Doping Agency with taking performance-enhancing drugs, in connection with the Bay Area Laboratory Co-operative (BALCO).
In a statement on the CAS website, it emerged that former double world champion Kelli White, who is also serving a two-year ban after admitting doping, testified against the pair claiming they both admitted using prohibited substances provided by BALCO.
As well as the suspensions, effective from June 6 this year, all results, rankings, awards and winnings obtained by Montgomery since March 31, 2001 and Gaines since November 30, 2003 will be cancelled.
This means Montgomery will no longer be credited as a former world record holder as he set his mark in Paris in September 2002.
He will also relinquish the silver medal he won in the 100m at the 2001 World Championships and the gold claimed by the 4x100m sprint relay.
The pair were not charged because of a positive drugs test but based on information gleaned from materials taken in raids on BALCO, already accused of being the source of the previously undetectable designer steroid THG (tetrahydrogestrinone).
The pair had declined arbitration by the USADA, instead going directly to CAS whose decision is final without recourse to appeal.
BALCO head Victor Conte, sentenced to four months in prison in October after pleading guilty to steroid distribution, said last year he had supplied Montgomery and partner - triple Olympic champion Marion Jones - with THG, EPO (erythropoietin) and insulin.
The scandal broke when Montgomery and Jones' former coach Trevor Graham anonymously sent a syringe containing a new steroid to the USADA and it was identified as THG.
A federal probe was launched into the California laboratory in 2003 and the fall-out engulfed some of athletics' top names.
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