The angiotensin II receptor blocker (ARB) telmisartan has a molecular structure that confers it partial agonist properties similar to those of peroxisome proliferators-activated receptor-gamma molecule, which is thought to modulate tissue response to insulin. In order to investigate the effects of telmisartan on insulin sensitivity and glucose metabolism, we enrolled 14 hypertensive patients under treatment with ARB other than telmisartan who had insulin resistance [homeostasis model for insulin resistance (HOMA-IR)>2.0] but no severe glucose tolerance (HbA1c<6.5%), and HOMA-IR was compared before and after the displacement by telmisartan. We also enrolled 27 obese (body mass index>25kg/m(2)) and hypertensive patients with type 2 diabetes under treatment with ARB other than telmisartan, and HbA1c was assessed before and after the displacement by telmisartan. The telmisartan significantly improved HOMA-IR in hypertensive patients and also significantly decreased HbA1c in type 2 diabetic patients especially in the patients with poor glycemic control (HbA1c>==8.0%). These results indicate that telmisartan improves insulin resistance and gives beneficial effects in hypertensive patients with type 2 diabetes and a poor glycemic control.