A Unitarian concept of shock has been proposed based upon theoretical physiologic grounds and supported by experimental and clinical data. This concept depicts shock as a defect in effective tissue perfusion, related to a decrease in cardiac output and organ blood flow and an increase in peripheral resistance. Restoration of cardiac output and organ blood flow by maintenance of effective circulating blood volume (central venous pressure, 10 cm. H2O, blood volume, 80 ml./kg. ) in association with digitalization when indicated will be effective in most patients in shock. In the remaining patients in which resistance in the cutaneous and visceral microcirculation remains elevated (pale, cool extremities and reduced urinary output), increased blood flow can be promoted in these areas by use of drugs which decrease vasoconstriction by blocking alpha-receptors ( phenoxybenzamine, phentolamine, chlorpromazine) or decrease resistance to flow by yet unknown means ( massive doses of glucocorticosteroids ) or decrease resistance by beta-receptor stimulation ( isoproterenol ) and consequent dilatation of the microcirculation of the muscles, while also stimulating the same receptors in the heart to increase the force and rate of cardiac contraction. In view of the dismal results obtained by vasopressors, alpha-receptor stimulators such as Levarterenol and Aramine, the use of these substances should be abandoned as the only form of treatment in shock.