1. Urinary excretion of dopa, catecholamines and their metabolites (vanillylmandelic acid, methoxycatecholamines, 3-methoxy-4-hydroxyphenylglycol and homovanillic acid) were studied in eighty patients with essential hypertension and in twenty-five healthy control subjects.
2. Increased urinary excretion of catecholamines, dopa and catecholamine metabolites was found in a proportion of cases.
3. The relationship between urinary excretion of catecholamine metabolites and the excretion of dopa and noradrenaline was studied.
4. In view of the suggested significance of 3-methoxy-4-hydroxyphenylglycol as an index of brain catecholamine metabolism, particular attention was paid to urinary excretion of this metabolite in the subjects under study.