1. The 24 h urinary excretion of noradrenaline and adrenaline is significantly lower in recumbent than ambulant normal subjects.

2. A diurnal variation exists in catecholamine excretion, the lowest values occurring during sleep.

3. Diurnal variation in sodium excretion parallels that in noradrenaline and adrenaline loss but the cycles can be separated by acute alterations in sleep/awake pattern.

4. Diurnal variation is lost during exercise, after myocardial infarction and was absent pre-operatively in a patient with a phaeochromocytoma.

5. Acute alterations in renal blood flow, diuresis, natriuresis and urinary acidification do not alter catecholamine excretion significantly.

6. Urinary catecholamine excretion is related to physical activity and wakefulness; the normal diurnal variation is easily overriden by sustained sympatho-adrenal activity. Alterations in renal function in exercise or after myocardial infarction do not account for the observed increases in catecholamine excretion.

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