Unfortunately, there is little hard evidence that anything other than complete avoidance can benefit asthmatic patients with a documented pet allergy.5 Since there appears to be a dose-response relationship between parameters of asthma control and exposure to allergen, it seems reasonable to keep the cat out of the bedroom, living room, and playroom. Washing pets has given variable results and must be repeated so frequently as to be impractical in most instances. Dust control measures prescribed for dust mite control, such as removal of carpets or use of a HEPA vacuum cleaner with double-reservoir bags, will also reduce the amount of settled allergen. Cat and dog allergen, as opposed to dust mite allergen, are often found on small particles that are easily airborne.1 This renders the use of air filtration devices attractive. Due to the small particle size of airborne allergens, HEPA cleaners are likely required. In addition to exclusion of the cat from the bedroom, a placebo-controlled, randomized study among adults with cat allergy using such a device installed in the bedroom failed to demonstrate any health benefit, despite a significant reduction in airborne allergen levels.6In contrast, a randomized, placebo-controlled crossover trial among cat- allergic children found an improvement in bronchial hyperresponsiveness.7 This study installed the air cleaners in both the bedroom and the living room, where allergen levels were higher.