Sterol metabolism studies using a combination of isotopic and chromatographic procedures were carried out in rats fed either a low-cholesterol stock diet or a stock diet containing 0.1% cholesterol. The primary bile acids, sodium taurochenodeoxycholate and sodium taurocholate, were added to the stock diets at a level of 0.5%, as required. Feeding sodium taurochenodeoxycholate and sodium taurocholate led to a decrease in acidic steroid synthesis, cholesterol turnover, and cholesterol balance, compared to controls. Sodium taurochenodeoxycholate feeding did not influence cholesterol absorption, but rats fed sodium taurocholate showed a twofold increase in cholesterol absorption as well as an accumulation of cholesterol in the liver. Rats receiving diets containing sodium taurochenodeoxycholate or sodium taurocholate plus cholesterol (0.1%) showed decreased acidic steroid synthesis, cholesterol turnover, and cholesterol balance, compared to the corresponding controls (Group 2, high cholesterol diet). Significantly larger amounts of cholesterol were absorbed in the taurocholate group (34.1 mg/day); these animals increased their concentrations of cholesterol in liver and plasma. The rats fed taurocholate plus 0.1% cholesterol differed from those fed taurochenodeoxycholate plus 0.1% cholesterol in the following respects: a) increased cholesterol absorption (35%), and b) accumulation of cholesterol in liver and plasma.