A study on the pressor response to various tests of sympathetic stimulation has been performed in 36 young subjects, 9 with labile hypertension and 27 normotensive. All have been studied with "tilt test", "cold pressor test" and "mental arithmetic stress". In the labile hypertensive subjects the "tilt test" induced increases of the systolic and diastolic pressure significantly higher than in the normotensives. The "cold pressor test" produced an increase of the arterial pressure and of the heart rate significantly lower in the labile hypertensive than in the normotensive. The pressure responses and the changes of the heart rate produced by the "mental arithmetic stress" did not show significant differences in the two groups of patients studied. The results are discussed.