Cape Town - FIFA says doping samples from World Cup players in South America are arriving at a laboratory in Switzerland within 33 hours.
FIFA and the World Anti-Doping Agency-accredited lab in Lausanne are under time pressure to test samples before a player's next match several days later.
Testing for the World Cup in Brazil is being done in Lausanne because WADA stripped the Rio de Janeiro lab's status for repeated errors.
All 736 players at the World Cup will provide pre-tournament blood and urine samples.
FIFA chief medical officer Jiri Dvorak says the first 750 samples have arrived in Switzerland "from several Latin American countries in less than 33 hours."
Dvorak says all samples arrived in good condition in cooled transit boxes.
Two players from each team are randomly chosen to give samples after each match. Scientists in are preparing to test samples around the clock to make sure any positive tests are acted on before a player's next match.
"We will make every effort to provide FIFA with the results prior to the next game," lab director Martial Saugy said.
Argentina great Diego Maradona was the last player caught doping at the World Cup - at the 1994 tournament in the United States.
Maradona tested positive for five types of the stimulant ephedrine after playing in Argentina's second group match. He was withdrawn from the tournament before being suspended.
At the Confederations Cup in Brazil last year, a player from Tahiti tested positive for a decongestant and was banned by FIFA for six months.
FIFA suspended three players from Peru, Jamaica and Zimbabwe for positive doping tests during qualifying for this year's World Cup. In a fourth case, a Moroccan player was suspended after a positive test for cannabis.
Peru midfielder Joel Sanchez received the most serious sanction, a two-year ban, after testing positive for the banned stimulant methylhexaneamine after a match against Bolivia in October 2012.
Last month, Sanchez's appeal was heard at the Court of Arbitration for Sport. A verdict is expected within weeks.