1. Ten patients with essential hypertension and ten healthy men were submitted to mental stress consisting of Kraepelin's arithmetic test combined with noise. Concentrations of plasma and urine catecholamines and of their metabolites as well as plasma renin activity before and after the test were studied.
2. In both groups a significant increase of noradrenaline and adrenaline in blood and noradrenaline in urine was observed. The urinary excretion of dopamine fell significantly in both groups after stress.
3. After mental stress a significant increase in urinary excretion of 3-methoxy-4-hydroxyphenylglycol was observed in both groups. The excretion of vanillylmandelic acid decreased significantly only in healthy subjects.
4. The plasma renin activity rose significantly in both groups but the increase was more pronounced in healthy subjects.