High-density lipoprotein (HDL) has a protective effect against atherosclerosis. Therefore, a compound that elevates the plasma HDL cholesterol (HDL-C) levels is expected to be a promising anti-atherosclerotic agent. We discovered a novel compound, R-138329, that increased HDL-C by 41% in normolipidemic hamsters at a dose of 100mg/kg. To investigate the mechanism of action of R-138329, we examined the effect of R-138329 on the clearance of [(3)H]cholesterol ether ([(3)H]COE)-labeled and [(125)I]-labeled HDL in mice. R-138329 delayed the clearance of [(3)H]COE-labeled HDL and reduced accumulation of tracer HDL in the liver, whereas the clearance of [(125)I]-labeled HDL particles was unaffected by the compound. In vitro analysis showed that R-154716, a metabolite of R-138329, dramatically inhibited the uptake of [(3)H]COE-labeled HDL in McA-RH 7777 rat hepatoma cells. Furthermore, 100 nM of R-154716 completely inhibited [(3)H]COE-labeled HDL uptake induced by overexpression of scavenger receptor BI (SR-BI) in HEK293 cells. Taken together, these findings suggest that the mechanism by which R-138329 elevates HDL-C in vivo is principally involved in the inhibition of SR-BI-mediated selective lipid uptake in the liver.