Objective: To study the influence of the adrenergic system, fasting serum insulin level and insulin sensitivity on systolic (SBP) and diastolic blood pressure (DBP) in young individuals. Design and methods: In a population survey we measured SBP and DBP (using the London School of Hygiene sphygmomanometer) and fasting levels of serum catecholamines, serum insulin and insulin sensitivity in 383 randomly recruited subjects (mean age 25.0 years) of both sexes. Insulin sensitivity was estimated from a combined intravenous glucose and tolbutamide tolerance test and calculated using Bergman’s minimal model. Confounders were body mass index, waist: hip ratio, maximal aerobic capacity, age, sex, and consumptions of tobacco and alcohol. Results: In a multiple regression analysis including the above factors, the most important determinant of SBP, after sex, was the plasma adrenaline level (partial correlation coefficient, rp = 0.23, P<0.01). No significant association was found between plasma noradrenaline level and SBP. A significant association was found between plasma adrenaline level and DBP in females only (rp = 0.15, P<0.05). Overall, the plasma adrenaline level was more important than the plasma noradrenaline level. Fasting serum insulin level and insulin sensitivity were each significantly correlated with both SBP and DBP in univariate analyses, but not in a multiple regression analysis. A family history of hypertension was associated with higher SBP level, body mass index and fasting serum insulin level, and with lower insulin sensitivity, but with no difference in circulating plasma adrenaline or noradrenaline compared with individuals without a family history. In a multiple regression analysis with the above confounders, no significant association between SBP and plasma adrenaline level could be found in either sex for subjects with a family history of hypertension. Both male (rp = 0.41, P<0.001) and female (rp = 0.18, P<0.05) subjects with no history of family hypertension had a significant association between SBP and plasma adrenaline level in a multiple regression analysis. Conclusion: In young healthy Caucasians adrenergic activity is an important determinant for SBP. The importance of fasting serum insulin level and insulin sensitivity on blood pressure level is minor when confounders are considered.