Female Nagase analbuminemic rats and Sprague-Dawley rats were fed purified diets with or without 1% cholesterol and containing either soybean protein or casein. After consuming the cholesterol-free diets, the analbuminemic rats had significantly higher plasma cholesterol and triglyceride concentrations than the Sprague-Dawley rats. The higher plasma cholesterol levels were essentially in the low density and high density lipoproteins. Based on the fact that the analbuminemic rats excreted more bile acids in feces it is possible that the higher baseline plasma cholesterol concentrations in Nagase analbuminemic rats were partly caused by overproduction of cholesterol. The Nagase analbuminemic rats displayed a greater cholesterolemic response to cholesterol feeding than Sprague-Dawley rats, but only if casein was the protein source in the diet. Casein vs. soybean protein in either cholesterol-free or high cholesterol diets reduced bile acid excretion in Sprague-Dawley but not in Nagase analbuminemic rats. The increased sensitivity to casein plus cholesterol feeding in Nagase analbuminemic rats may be caused by a lack of inhibition of de novo cholesterol synthesis.