In a double-blind, placebo-controlled, randomized crossover study, 15 stable mild hyperglycemic patients without treatment and with features of metabolic syndrome were treated with cerivastatin (0.4 mg/day) or placebo for 3 months. The insulin sensitivity index during the euglycemic-hyperinsulinemic clamp (EHC; 5.4 mmol/l; 80 mU x m(-2) x min(-1)) was increased by cerivastatin treatment (66.39 +/- 3.9 nmol x lean body mass [LBM](-1) x min(-1) x pmol(-1) x l(-1)) as compared with placebo (58.37 +/- 3.69 nmol x LBM(-1) x min(-1) x pmol(-1) x l(- 1); P < 0.01) by 13.7%. Glucose oxidation during EHC was significantly higher with statin treatment (16.1 +/- 1.37 micromol x LBM(-1) x min(-1)) as compared with placebo (14.58 +/- 1.48 micromol x LBM(-1) x min(-1); P < 0.05). During hyperinsulinemia (approximately 800 pmol/l) in EHC steady-state, lipid oxidation was significantly decreased and respiratory quotient was significantly increased with statin treatment (0.33 +/- 0.05 mg x LBM(-1) x min(- 1), 0.94 +/- 0.01) as compared with placebo (0.48 +/- 0.06 mg x LBM(-1) x min(-1), 0.91 +/- 0.01; P < 0.01 and P < 0.05, respectively). During statin treatment, the first-phase insulin response increased from 2.07 +/- 0.28 to 2.82 +/- 0.38 pmol x l(-1) x pmol(-1) (P < 0.05). The second phase of insulin responses examined by C-peptide and insulin levels averaged during the hyperglycemic clamp (20 mmol/l) was unchanged. In conclusion, this study demonstrates that 0.4 mg cerivastatin therapy improves first-phase insulin secretion and increases insulin-mediated glucose uptake and respiratory quotient in the early state of obese type 2 diabetes.