In our study of experimental endotoxin shock we tried therapeutic control of reversible acute endotoxin shock. In a standard model in the dog, in which endotoxin shock had been induced by intravenous injection of E. coli endotoxin dosed 1.75 mg/kg, the effects of hydrocortisone and dopamine administered concurrently were investigated. It was found that endotoxin shock elicited primarily haemodynamic alterations; arterial hypotension, reduction of renal arterial blood flow, elevation of central venous flow, decrease in left ventricular pressure, and vasodilatation. Dopamine plus hydrocortisone prevented development of alterations, primarily of haemodynamic ones, already in the initial phase of shock. Dopamine plus hydrocortisone raised the survival quota of animals in endotoxin shock, enhanced the renal arterial blood flow, maintained the diuresis, enhanced myocardial contractility, and elevated left ventricular blood pressure. After higher dosages of dopamine the peripheral blood pressure rose as well. The dosage of dopamine has to be adjusted with respect to the actual state of haemodynamics. The developing tendency to acidosis was not brought under control within the three-hour monitoring period.