World anti-doping chief Dick Pound defended testing procedures that have come under fire since Marion Jones was cleared of a doping offence, saying she had been given the benefit of doubt.
"The system is working in the matter as it should in the case of Marion Jones," said Pound during a teleconference ahead of the World Anti-Doping Agency's (WADA) executive board meeting at the weekend.
"The 'B' did not confirm the 'A' sample, therefore there is no doping offence. The rights of the athletes in these cases are fully protected and that's the way the system works.
"We would rather let somebody, who may be guilty, go free rather than sanction someone, who shouldn't be sanctioned."
High profile doping cases involving Americans Jones and Tour de France winner Floyd Landis are likely to dominate discussion at WADA's executive committee meetings, which will approve the 2007 list of prohibited substances and testing methods.
Triple Olympic champion Jones was cleared of doping earlier this month when her 'B' sample tested negative for the banned blood-boosting drug erythropoietin (EPO).
The sprinter's initial sample had tested positive at the US championships in Indianapolis in June. The 30-year-old could have faced a two-year ban from the sport had the second sample tested positive.
Following the negative result of the 'B' sample, questions have been raised about the reliability of testing procedures.
Pound said he had confidence in the testing protocol and the laboratories that carry them out but a routine investigation would take place to try and determine why the samples produced contradictory results.
"We have asked the laboratories involved to provide us with the complete material which is our standard operating procedure when the 'A' and 'B' samples don't match," he said. "We're confident about the test, no question about that."
Landis's 'excuses'
Landis asked a US Anti-Doping Agency (USADA) review board this week to dismiss doping charges against him arguing that tests conducted on his two urine samples from stage 17 of the Tour de France did not meet the established WADA criteria for a positive doping offence.
Pound, however, made it clear that Landis faced several hurdles before he would be able to clear his name.
"A test is conclusively considered positive when the 'A' and 'B' sample both confirm the presence of a prohibited substance.
"Just because you see a whole bunch of excuses put forward by an athlete or someone on his or her behalf doesn't mean that a responsible anti-doping agency is just going to roll over and play dead."