To clarify the genetic basis of insulin resistance in hypertension, case-control association studies were performed to examine candidate genes for insulin resistance in hypertension. Since the main site of insulin resistance in hypertension is glycogen synthesis in skeletal muscle, genes that encode molecules involved in this pathway, i.e. insulin receptor (INSR), insulin-responsive glucose transporter (GLUT4) and glycogen synthase (GSY), were studied. In addition, since recent studies suggest the contribution of beta3 adrenergic receptor to the insulin resistance syndrome, the gene encoding beta3 adrenergic receptor (ADRB3) was also studied. Frequency of homozygotes for common C allele of a microsatellite polymorphism in the INSR gene was higher in the hyperinsulinemia group, but not in the normoinsulinemia group of hypertensive patients than in normotensive control subjects. Insulin sensitivity, however, was not significantly different between hypertensive patients with C/C genotype and those without this genotype. No significant differences were observed in the distribution of alleles or genotypes of the GLUT4, GSY and ADRB3 genes between hyperinsulinemia and normoinsulinemia groups of hypertensive patients or between these groups and the control group. These data suggest that the INSR polymorphism is associated with hyperinsulinemia, but not with insulin resistance, in hypertension.