Two dead birds were discovered at the Olympic equestrian venue in Hong Kong, and authorities were testing whether the animals were infected with the dangerous H5N1 bird flu virus.
The birds were found last week, said Mark Pinkstone, head of equestrian preparation operations and media services, on Monday.
Bird flu doesn't pose a threat to horses, but it can sicken humans.
Hong Kong, which has struggled with the bird flu for years, suffered its biggest outbreak in 1997, when it killed six people.
The Olympic equestrian events, to be held from Aug. 9-21, were moved from Beijing to the former British colony because of a rash of equine diseases and substandard quarantine procedures on the mainland.
Hong Kong has much experience handling foreign horses due to its prominent horse racing scene, but the city's sweltering summer heat and humidity remain a major concern.