Obesity, hypertension and obesity-related hypertension are growing health problems.Importantly, while frequently associated, not all obese subjects have hypertension.It is widely recognized that heightened sympathetic nerve activity and insulin resistance (or hyperinsulinemia) relate to obesity and hypertension.However, the precise relationships between insulin resistance and heightened sympathetic nerve activity in obesity and hypertension remain uncertain.Many investigators have indicated that insulin resistance may play a major role in obesity, hypertension, and obesityrelated hypertension, and heightened sympathetic nerve activity accompanies insulin resistance.On the other hand, some investigators have reported in a series of longitudinal studies that heightened sympathetic nerve activity may be a prime mover for obesity, hypertension, and obesity-related hypertension, and insulin resistance may play an ancillary role.We have found blunted sympathetic nerve responses to insulin stimulation only in insulin resistant subjects, suggesting that the relationships between insulin resistance and sympathetic nerve activity might be different due to the stage of obesity, hypertension, or severity of insulin resistance.Both hypotheses emphasize the close linkage between insulin resistance and heightened sympathetic nerve activity; however, which is the prime mover for obesity or hypertension remains unknown.