Recent work in allergy has emphasized the importance of the inhaled substances in the production of bronchial asthma and other allied disorders. Many patients exhibiting sensitivity to the inhaled proteins are sensitive to house dust, either alone or in conjunction with other proteins of this type. In Cooke's1series of 327 cases, 69.8 per cent, reacted to the inhaled proteins, and of these 109, or 33 per cent., were sensitive to house dust. Because of the importance of the inhaled substances in general and house dust in particular it seemed appropriate to attempt to devise a method whereby these patients could be studied under controlled conditions of environment. It soon became apparent that observations made under these conditions should incorporate records of room temperature and relative humidity and these, therefore, were included. The purposes of this study may conveniently be stated under the following headings and the reasons for