Partial peroxisome proliferator-activated receptor-gamma (PPAR-gamma) agonists are known to decrease insulin resistance. Experimental studies have shown that the angiotensin type 1 receptor blocker (ARB) telmisartan has a PPAR-gamma-activating property, but there does not appear to be a class effect. To test telmisartan's clinical importance, we here investigated its effect on insulin resistance in hypertensive patients with metabolic syndrome (MetS) in comparison with another ARB, losartan. A total of 42 hypertensive MetS patients (29 female, 13 male) were included (mean age: 50 9, range: 20-70 years). NCEP-ATP III criteria were used for the diagnosis of MetS. Patients were randomized to receive either telmisartan 80 mg/day (n = 21) or losartan 50 mg/day (n = 21) for 8 weeks. Biochemical assessments were made at baseline and at the end of the 8 weeks. Insulin resistance was evaluated by using homeostasis model assessment of insulin resistance (HOMA-IR). Both groups had similar reductions in systolic and diastolic pressures (p > 0.05). HOMA-IR did not change significantly in either group throughout the study. In the telmisartan group, the mean HOMA-IR at baseline and at the end of the study were 1.9 +/- 07 and 1.9 +/- 0.5, respectively. The figures for the losartan group were 1.8 +/- 0.6 and 1.8 +/- 0.6, corresponding. In conclusion, in contrast with the reports that telmisartan may decrease insulin resistance by an effect associated with its molecular structure, 8 weeks of telmisartan treatment in the present study had a neutral effect on insulin resistance in hypertensive MetS patients, and similar results were obtained for losartan.