Air-cleaning devices are in widespread use and manufacturers claim many benefits from the use of their devices, including the releaf of allergic respiratory symptoms. In 1987, a commmittee reviewed the available literature on the technical and clinical efficiency and concluded that the role of indoor air-cleaning devices is limited. Since then, a small number of double-blind, placebo-controlled trials were done, allowing some differentiation of these recommendations. In particular, pet allergic asthmatic individuals might have a clinical benefit under certain conditions. In this review, we discuss the conclusions and limitations of these studies. It is clear, however, that the most important health benefit will be achieved by eliminating the source of the allergen from the indoor environment.