The role of insulin and dopamine on blood pressure and renal sodium excretion was evaluated in 10 obese hypertensive patients. Essential hypertensive subjects (age 49.7±7.7) with at least 26.0kg/m² obesity were hospitalized and a 2000k cal diet for 7 days (control periods) followed by a 800 k cal for 21 days were given. Salt intake was maintained at 10 g/ day throughtout this study. Mean blood pressure (MBP), plasma insulin (IRI), urinary dopamine and fractional excretion of sodium (FENa) were measured in both diet periods. Body mass index significantly decreased from 31.6±4.6kg/m² to 28.6±4.1kg/m² after weight reduction (P<0.001). MBP significantly lowered from 112.8±14.1mmHg to 100.4±12.4 mmHg (P<0.01) and IRI from 9.11±5.0 μU/ml to 6.3±5.5 iU/ml (P<0.001) after weight loss. We observed a significant correlationship between ΔMBP and ΔIRI (r=0.754, P<0.01). Also, we observed a significant correlationship between ΔMBP and ΔFENa (r= -0.835, P<0.01). A significant relationship was observed between urinary excretion of sodium and urinary excretion of dopamine (r=0.507, P<0.05). We concluded that sodium retention and increase of sympathetic nervous activity by hyperinsulinemia might play an important role of hypertension, and blood pressure reduction by weight loss resulted from decreased insulin and increased excretion of sodium in obesity hypertension.