The haemodynamic measurements made in two cases of proved phaeochromocytoma are described. In both the systemic vascular resistance (SVR) was markedly increased and was associated with a decreased preload. In one case, phentolamine infusion, when lowering the SVR, produced a marked decrease in the cardiac index resulting in a state of hypovolemic shock. This was successfully treated by the administration of plasma expanders. The data tend to indicate that haemodynamic measurements in cases of phaeochromocytoma could be both of diagnostic and therapeutic interest.