Fecal sterols of human subjects, aged 0-80 years old, were analyzed by thin-layer chromatography and gas-liquid chromatography, in order to clarify the role of intestinal flora in the metabolism of cholesterol. It is known that cholesterol is transformed into coprostanol, an unabsorbable sterol, by the intestinal flora. The coprostanol was not detected in the meconium and neonatal feces. This sterol was detected in the feces of subjects over 2 years old and the content increased with age. In contrast, the content of cholesterol decreased with age, so that the coprostanol/cholesterol ratio increased. Over 92% of the cholesterol in feces was non-esterified, indicating the active sterol metabolism by the intestinal flora, because cholesterol is transformed into coprostanol only when cholesterol is free form. The feces of aged subjects contained some unidentified neutral sterol-like substances other than cholesterol, coprostanol and plant sterols, suggesting that the sterol metabolism is complicated by many species of intestinal flora such as Clostridium. The longer transit time through the gut of aged subjects than younger subjects may also contribute to the complex metabolism of sterols by intestinal flora. It is suggested that the transformation of cholesterol into coprostanol and other sterol metabolism by intestinal flora may play an important role in the sterol metabolism of whole body.