SummaryThe effects of spinach leaf protein concentrate (SPPC) on serum and liver lipid concentrations and on serum free amino acid concentrations were examined in rats fed a cholesterol-free diet contain ing 2 and 10% fats. The serum total cholesterol, triacylglycerol and phospholipid concentrations in the rats fed an SPPC diet containing 2% corn oil were significantly lower than those of the rats fed a corresponding casein diet. When 10% corn oil or lard was used, the serum cholesterol lowering effect of the SPPC became insignificant, but the serum and liver triacylglycerol concentrations were kept at significantly lower levels. Both the amounts of fecal neutral steroids and bile acids were significantly higher in the rats fed the SPPC than those of the casein-fed rats. The concentrations of serum threonine, serine, glutamine, glycine, cystine, and isoleucine were significantly higher in the rats fed the SPPC diet contain ing 2% corn oil compared with those of the control rats, but when the dietary fat was raised to 10%, only glycine showed a higher serum concentration. These results indicate that the SPPC has a stronger cho lesterol-lowering effect at a lower dietary fat level, 2%, and the activity is partly due to the inhibition of intestinal absorption of cholesterol and bile acid, and partly due to an increase in the concentration of some of the serum amino acids. Key Words spinach leaf protein concentrate, cholesterol-lowering effect Plant protein has received much attention because it generally exerts a hypo cholesterolemic effect compared with animal protein. Soybean, sunflower, rice and pea protein isolates (1-10), and Italian ryegrass and alfalfa protein concentrates (11) are the representative plant proteins shown to have a hypocholesterolemic effect when compared with casein. However, the cholesterol-lowering effect of other plant protein isolates, especially the vegetable protein isolates with high purity, have not yet been fully examined. Spinach leaf protein concentrate (SPPC)