Bronchiolitis is a common performance decreasing disease in horses (Bracher et al, 1991¸Dixon et al, 1995) Its medical treatment includes inhalation therapy with corticosteroids and b2-adrenoceptorer stimulators. Use of both these medicines is prohibited for sport horses and athletes. Because the facemasks used for inhalation therapy are not airtight, there is a risk for leakage of these medicines. We wanted to see if cross exposure of nearby horses can result during normal recommended treatment of a horse, and assess if this could result in doping positive urine sample from the person treating the horse and from horses in the same airspace. We did a pilot study with four healthy horses. The experiment was divided into four parts.