The effect of cholesterol feeding on bile acid turnover and neutral fecal steroid excretion was studied in rabbits and human subjects. In rabbits the addition of 1% cholesterol to a low fat pellet diet (on the average 700 mg of cholesterol per day) caused a marked increase of the serum cholesterol level but a reduction of the turnover and the fecal elimination of deoxycholic acid. On the subsequent feeding of a semisynthetic cholesterol free diet, the serum cholesterol level decreased in spite of a further reduction of the fecal bile acid excretion. When human subjects received a diet containing egg yolk lipids, which provided 1.4 g cholesterol per day, the serum cholesterol level increased moderately over the control values, but there were no consistent effects on either the biliary bile acid composition or on the turnover of cholic acid. The amount of cholesterol excreted as neutral fecal steroids during the cholesterol feeding period corresponded on the average to 80 and 77% of the amount of cholesterol given to rabbits and human subjects respectively. Cholesterol and the plant sterols β-sitosterol and methylcholesterol were metabolized into neutral compounds that were the same in rabbit and in human feces. Rabbit feces contained proportionally more 5α-sterols than human feces.