The influence of various statins on low-density-lipoprotein (LDL)-particle phenotype has been reportedly trivial or moderate. We assessed the effect of rosuvastatin (the newest statin available) on the LDL subfraction profile in patients with primary hyperlipidemia. One hundred and twenty patients with primary hyperlipidemia without evidence of cardiovascular disease were randomized to therapeutic lifestyle modification ('control' group, N=60) or therapeutic lifestyle modification plus rosuvastatin 20 mg/day (N=60). Laboratory evaluation was performed at baseline and 12 weeks post-treatment. LDL subfraction analysis was carried out electrophoretically using of high-resolution 3% polyacrylamide gel tubes and the Lipoprint LDL System. Rosuvastatin induced a redistribution of LDL-cholesterol from small-dense LDL particles to large-buoyant ones and increased the mean LDL particle size. This beneficial effect was observed only in patients with baseline triglyceride levels >or=150 mg/dl (mean LDL particle size 255+/-7 A vs 260+/-5 A, P<0.01), whereas the LDL subfraction profile was not altered in those with triglyceride levels <150 mg/dl. Stepwise multivariate linear regression analysis revealed that baseline triglyceride levels (R(2)=0.29, P=0.001) followed by baseline insulin resistance as assessed by the HOmeostasis Model Assessment (HOMA) (R(2)=0.25, P=0.001) were independently associated with the rosuvastatin-induced increase in the mean LDL particle size. In conclusion, rosuvastatin at 20 mg/day favorably modified the relative distribution of LDL-cholesterol distribution on LDL subfractions as well as on the mean LDL particle size in patients treated for primary dyslipidemia. Baseline triglyceride levels as well as baseline HOMA-index were found to be the major predictors of this beneficial action of rosuvastatin.