There will be 229 horses in the Olympics and 75 in the Paralympics. Testing will be conducted in Hong Kong from July 26, and the tests needed will amount to about six times the lab's usual workload.

Testing takes place at three stages.

In the post-arrival elective testing, or PAET, which is being offered for the first time at the Olympics, competitors can voluntarily test their horses for residues of 66 legitimate therapeutic medications before the competitions to prevent inadvertent infringements. If a test returns positive, competitors may have to switch horses.

During and after the competitions, the FEI, the governing body for equestrian disciplines, will send medal winners and other horses for spot checks to test for therapeutic and non-therapeutic drugs.

The lab aims to process tests during and after the competitions in seven and 12 days for negative and positive results respectively, to beat the 2004 Athens Olympics time by 20 and 11 days. It will test at least 50 horses, 10 more than at Athens. The PAET will take three or four days.

'Although this is the first time that we are doing the Olympics, we are already very experienced,' Dr Wan said, noting they tested horses for the Asian Games in Qatar in 2006 and South Korea in 2002 and can test 150 horses in one race day within four or five hours.

Yesterday, chemists were seen conducting liquid, solid and gas tests on urine and blood samples under CCTV cameras, and working in the refrigerated storage room, which is accessible only by one person at a time by a magnetic key card.

There are four FEI reference laboratories in the world. The others are in Paris, New York and Sydney.