OBJECTIVES: The purpose of this analysis was to compare concentrations of low-density lipoprotein cholesterol (LDL-C), non-high-density lipoprotein cholesterol (HDL-C), and apolipoprotein B (apoB) before and during statin therapy. BACKGROUND: Reducing LDL-C to a pre-determined goal may still leave an excess of atherogenic lipoproteins, as reflected in apoB levels. METHODS: The MERCURY II (Measuring Effective Reductions in Cholesterol Using Rosuvastatin therapY II) trial examined the effects of statin treatment in patients with high coronary heart disease (CHD) risk, LDL-C > or =130 and <250 mg/dl, and triglycerides <400 mg/dl. Therapy consisted of rosuvastatin (10 or 20 mg), atorvastatin (10 or 20 mg), or simvastatin (20 or 40 mg). The apoB and LDL-C or non-HDL-C at baseline and after 16 weeks of therapy were compared using linear regression. RESULTS: In untreated patients, the apoB target of <90 mg/dl was roughly equivalent to an LDL-C level <100 mg/dl and a non-HDL-C level <130 mg/dl, which is consistent with existing apoB and lipoprotein guidelines. However, during statin therapy, to reach an apoB target of <90 mg/dl it was necessary to reduce non-HDL-C to <100 mg/dl or to reduce LDL-C to <70 mg/dl (in high-triglyceride patients) or <80 mg/dl (in lower-triglyceride patients). The tight correlation seen for non-HDL-C with apoB while on statin therapy (R(2) = 0.92) implies that non-HDL-C may be an acceptable surrogate for direct apoB measurement. CONCLUSIONS: These data are consistent with the more aggressive cholesterol goals suggested for CHD patients, because achieving such targets also reduced apoB to the recommended level. (Mercury II-Compare the Efficacy and Safety of Lipid Lowering Agents Atorvastatin and Simvastatin With Rosuvastatin in High Risk Subjects With Type IIa and IIb Hypercholesterolemia; NCT00654407).