The authors present this monograph to condense the facts and to present certain practical applications of the anti-histamines. The volume is primarily clinical in orientation, but experimental studies leading up to the development of the histamine theory and the antihistamines are discussed. Clinical observations include the use of the antihistamines in respiratory allergy, the dermatoses and various miscellaneous and possibly allergic conditions. There is a thorough review of the toxic effects of the agents. The appendix lists 16 antihistamines, which are promoted under various trade names. This appendix should prove valuable to physicians in their attempt to distinguish between the claims for various antihistamines and should aid in identification of the specific agent employed.