BIBB 515 is a selective and potent inhibitor of OSC in vivo with an ED50 value of 0.2-0.5 and 0.36-33.3 mg/kg in rats and mice, respectively. 2, 3-Oxidosqualene cyclase (OSC) is an important enzyme in the biosynthesis of animal, plant, and fungal sterols. OSC catalyzes the conversion of (3S)-2, 3-oxidosqualene to lanosterol, a precursor to cholesterol, in mammals and fungi. Total cholesterol was reduced by 19% in normolipemic hamsters at a dose of 55 mg/kg/day for 11 days and 25% in hyperlipemic hamsters at a dose of 148 mg/kg/day for 25 days.