This small monograph consists largely of discussion and description of the clinical conditions associated with sudden or less abrupt lowering of blood pressure. Animal experimentation has not been developed in this field, if one judges by this work. No electrocardiographic tracings have been used. A few charts of daily blood pressure readings during infection are shown. The symptoms of syncope derived from the brain, eye, ear, blood and other viscera are discussed. Those arising from the heart and the associated observations are described. Various syndromes with acute hypotension as the central etiologic factors are pictured. Hypotension occurring in the course of other diseases is then discussed at length. One is impressed with the thoroughness of clinical study and the plausibility of theoretical argument, while the lack of exact physiologic measurement of the factors concerned is evident.