Vasoconstrictors are mainly used in acute hypotensive states, and they often succeed in bringing about at least a temporary increase in arterial pressure. Pressure is easy to measure, whereas tissue perfusion is not; but it is the latter that is the important variable, and a rise in pressure does not necessarily imply an improved circulation. In this review the human pharmacology of a variety of constrictors is surveyed. Abrief account of the abnormal physiology of hypotensive states is followed by an attempt to assess the contribution of vasoconstrictors to their management. It is concluded that, where benefit follows the use of a vasoconstrictor, it often comes from the cardiac stimulatory action of the drug rather than from a rise in blood pressure resulting from vasoconstrictor action.