Objective:The aim of this work was to study the insulin-like growth factor 1 (IGF1), a substance able to promote cell proliferation in vascular smooth muscle, in patients with mild-to-moderate hypertension and to analyse its relationship to sodium—lithium countertransport, a genetic marker of hypertension that is related to cardiovascular complications.Method:We studied 32 hypertensive subjects, some with left ventricular hypertrophy, and 14 healthy subjects. Fasting plasma IGF1 was measured by means of a radioimmunoassay after octadecylsilica chromatography and Na+-Li+countertransport was determined by the method of Canessa.Results:Hypertensive patients had higher values of both IGF1 and Na+-Li+countertransport. We found a positive correlation, irrespective of age, between IGF1 and Na+-Li+countertransport. The patients with left ventricular hypertrophy had significantly higher plasma IGF1 levels than those without left ventricular hypertrophy.Conclusion:Our results confirm a possible role for IGF1 in the cardiovascular complications of hypertension and emphasize its relationship to genetically determined factors.