We investigated the relationship between peroxisome proliferator-activated receptor gamma (PPARgamma) Pro12Ala substitution and insulin resistance in subjects with normal insulin secretory capacity, since it has been reported that PPARgamma may affect not only insulin resistance but also insulin secretion. We examined 81 Japanese male patients with untreated essential hypertension using the glucose clamp technique. We found 77 subjects with Pro/Pro and 4 subjects with Pro/Ala genotype, and the glucose disposal rate was not significantly different between the two groups. Fasting plasma glucose, fasting immunoreactive insulin, total cholesterol, HDL cholesterol, and triglyceride were not significantly different between the two groups. There were also no significant differences between groups in homeostasis model assessment of insulin resistance (HOMA-R) values, area under the curve (AUC) for plasma glucose, or AUC for IRI in 75 g OGTT. Because insulin sensitivity is likely to be determined by polygenic factors, we also investigated beta3 adrenergic receptor Trp64Arg polymorphism as a possible determinant of insulin resistance. In conclusion, no significant association was observed between PPARgamma2 substitution and insulin sensitivity in the present cohort of Japanese hypertensive patients.