The combined effects of pravastatin and probucol on high-density lipoprotein (HDL) apolipoprotein (apo) A-I kinetics in cholesterol (Ch)-fed rabbits were investigated. Japanese White rabbits were treated with 0.15% pravastatin and 0.5% Ch (group 1) or 0.15% pravastatin plus 1% probucol and 0.5% Ch (group 2) for 2 months. After treatment, the serum total cholesterol levels in groups 1 and 2 had significantly (p<0.01) increased (37.4±6.7 mg/dl vs 117.1±46.4 mg/dl, and 31.4±4.9 mg/dl vs 143.0±84.5 mg/dl, respectively). The serum HDL-cholesterol levels in both groups decreased (18.2±2.8 mg/dl vs 16.2±3.7 mg/dl, p<0.01 for group 1; 18.2±1.9 mg/dl vs 15.5±4.5 mg/dl, ns for group 2). Apo A-I kinetics were assessed by injecting ¹²⁵I-labeled HDL intravenously into both groups of rabbits, and taking blood samples periodically for 6 days. Kinetic parameters calculated from apo A-I specific radioactivity decay curves showed that the apo A-I fractional catabolic rates in rabbits fed pravastatin and Ch (group 1) were significantly less than those in rabbits fed pravastatin plus probucol and Ch (group 2)(0.546±0.017 /day vs 0.730±0.126 /day, p<0.05), while the synthetic rate of apo A-I was lower in group 2 than in group 1 (14.76±1.71 mg/kg per day vs 11.21±2.38 mg/kg per day, respectively, p<0.1). These data indicate that pravastatin and probucol have different effects on HDL-apo A-I kinetics in a diet which includes cholesterol.