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Three patients with postural hypotension (two of the idiopathic type, one possibly due to familial dysautonomia) were found to have not only the pathognomonic postural hypotension, without rise in heart rate, cardiac output and peripheral vascular resistance, but also a similarly abnormal regulatory mechanism on ergometric stress when recumbent. There was a delayed-response to the bloodpressure fall on Valsalva a manoeuvre, and the blood volume was reduced. A combined effect of these factors explains that these patients have a more marked impairment of physical capcity than might be expected merely from the orthostatic hypotension. The actions of noradrenaline, adrenaline, phenylephrine, isoproterenol, angiotensin and tyramine on blood pressure and heart rate were different from normal. Plasma-renin activity was reduced in all three patients and could not be raised. Urinary excretion of adrenaline and noradrenaline was markedly diminished. Reactions to noradrenaline and tyramine, as well as the excretion pattern of the catecholamine metabolites suggest a disorder of active adrenaline liberation. Furthermore, different disorders of catecholamine metabolism underlie idiopathic orthostatic hypotension and familial autonomia. Therapeutic trials with fludrocortisone, beta-receptor blockers and levodopa brought improvement, but long-term results are not yet available.