We examined the effect of atorvastatin, an inhibitor of 3-hydroxy-3-methylglutaryl coenzyme A reductase, on the kinetics of apolipoprotein B-100 (apoB) metabolism in 25 viscerally obese men in a placebo-controlled study. Very-low-density lipoprotein (VLDL), intermediate-density lipoprotein (IDL), and low-density lipoprotein (LDL) apoB kinetics were measured using an iv bolus injection of [(2)H(3)]leucine. ApoB isotopic enrichment was measured using gas chromatography-mass spectrometry. Kinetic parameters were derived by using a multicompartmental model (SAAM-II). Compared with the placebo group, atorvastatin treatment resulted in significant (P < 0.001) decreases in total cholesterol (-34%), triglyceride (-19%), LDL cholesterol (-42%), total apoB (-39%), and lathosterol (-86%); VLDL-apoB, IDL-apoB, and LDL-apoB pool sizes also fell significantly (P < 0.002) by -27%, -22%, and -41%, respectively. This was associated with an increase in the fractional catabolic rates of VLDL-apoB (+58%, P = 0.019), IDL-apoB (+40%, P = 0.049), and LDL-apoB (+111%, P = 0.001). However, atorvastatin did not significantly alter the production and conversion rates of apoB in all lipoproteins. We conclude that in obese subjects, atorvastatin decreases the plasma concentration of all apoB-containing lipoproteins chiefly by increasing their catabolism and not by decreasing their production or secretion. This may be owing to up-regulation of hepatic receptors as a consequence of inhibition of cholesterogenesis.