Insulin resistance may play a role in the pathogenesis of essential hypertension. The purpose of the present study was to examine the relations of fasting serum insulin or C-peptide levels with hypertension and blood pressure (BP) in a stable homogeneous southern Chinese population with normal glucose tolerance. This community-based survey of adults aged > or = 30 years in Kin-Chen, Kinmen, was conducted by the Yang-Ming Crusade in 1992 and 1994. Data of fasting serum insulin and C-peptide from a total of 1,447 men and 1,800 women (mean age 46.7 years) were analyzed. Both continuous (by multiple regression) and categorical analyses (by analysis of covariance) were used. Fasting insulin concentrations (as independent variables) were significantly associated with log systolic BP (as outcome variables, coefficient = 0.000081, p = 0.0035) and log diastolic BP (as outcome variables, coefficient = 0.000098, p = 0.0006) after accounting for age, sex, body mass index, and waist-to-hip ratio. Similarly, fasting C-peptide concentrations were significantly associated with log systolic BP (coefficient = 0.023304, p = 0.0001) and log diastolic BP (coefficient = 0.032971, p = 0.0001). In categorical analyses, both fasting insulin and C-peptide concentrations were significantly different (insulin p = 0.01010, and C-peptide p = 0.0004) between hypertensive and normotensive subjects when the similar set of covariates were accounted for. In conclusion, both fasting serum insulin and C-peptide concentrations are significantly associated with BP in this homogeneous Chinese population with normal glucose tolerance.