Hyperinsulinemia and the associated increased sympathetic nervous activity have been proposed to implicate in the development of hypertension and obesity. The role of hyperinsulinemia in mediated resting energy expenditure (REE) in hypertensive obese subjects is not clear. The effect of weight loss on REE between hypertensive and normotensive obese women are also unknown. We measured fasting plasma glucose, insulin, lipids concentrations, REE and body composition by bioelectrical impedance methods before and after a weight loss program in 9 newly diagnosed hypertensive and 10 normotensive obese women. As compared with age-matched lean control women (n=14), obese subjects had higher fasting plasma glucose, insulin concentrations and REE values. However, these variables were not different between obese groups. Although REE and fasting plasma insulin concentrations correlated well in simple correlation (r=0.708, p<0.001), this relationship disappeared after adjusting for values of fat free mass (FFM). Weight loss for approximately 10% of initial weight led to significant decreases of blood pressure and fasting plasma insulin concentrations in both obese groups. Fasting plasma cholesterol, LDL cholesterol and triglyceride concentrations decreased in hypertensive obese individuals. Significant fall of REE in hypertensive group (p<0.05) and normotensive group (p<0.02) were observed following weight loss. However, the ratio of REE to FFM decreased significantly only in hypertensive subjects (114.6+/-5.2 KJ/day x Kg(-1) to 107.2+/-4.6 KJ/day x Kg(-1), p<0.05). In conclusion, obese women, either hypertensive or normotensive, had higher fasting plasma insulin concentrations and REE than those of lean controls, although these variables were not different between obese groups. No significant relation between fasting plasma insulin and REE could be found. Weight loss produced a significant decrease of REE/FFM only in hypertensive obese women. Further study to evaluate the effect of weight loss on energy expenditure in hypertensive obese subjects is necessary.