An anaerobic, gram-positive diplobacillus that reduces cholesterol to coprostanol was isolated from human feces and rat cecal contents. The isolates closely resemble a cholesterol-reducing organism isolated by Eyssen et al. (H. Eyssen et al., Eur. J. Biochem. 36:412-421, 1973) from a rat's cecum. These organisms would not form colonies and were isolated and cultivated in an anaerobic medium containing homogenized pork brains (naturally high in cholesterol). These organisms require free or esterified cholesterol for growth. They were isolated by serially diluting feces or cecal contents and inoculating brain medium. Colony-forming organisms, which did not reduce cholesterol, were eliminated by addition of inhibitory agents to the brain medium cultures. This serial dilution procedure was performed until a pure culture of a cholesterol-reducing organism was obtained.