Cat allergen exposure was performed in a room furnished with upholstered furniture, a blanket, and a cat litter box. The door was kept closed at all times, except when personnel or study patients were entering or leaving the room. The ventilation system was operating at all times except during cat allergen challenges. Two neutered adult cats were kept in the room at all times and were free to move about except during challenges, at which time they are placed in wire cages. Immediately before a challenge, the blanket was shaken vigorously to distribute cat allergen throughout the room.