Acarbose, a complex oligosaccharide of microbial origin, was added at levels of 100, 200 or 400 mg/kg to an atherogenic diet fed to New Zealand White rabbits. The rabbits consumed 75 g/day of each diet, thus the daily intake of Acarbose was 7.5, 15 and 30 mg. Rabbits fed 30 mg/day of Acarbose showed reduced levels of plasma cholesterol, intermediate density lipoprotein (IDL) and low density lipoprotein (LDL). Aortic sudanophilia was inhibited by 23% in rabbits fed 7.5 mg/day of Acarbose and by 43% in rabbits fed 15 or 30 mg/day. Acarbose had been shown previously to lower serum cholesterol and triglyceride levels in rats and mice. Our studies demonstrate that it also inhibits atherogenesis in rabbits fed 0.2% cholesterol.