The effects on hypercholesterolemia of dietary additions of cystine (Cys), methionine (Met), glycine (Gly), and a combination of Met and Gly to a 20% casein diet were studied in male Donryu rats subcutaneously implanted with an ascites hepatoma line of AH109A cells. The hepatoma-bearing rats fed the 20% casein diet lapsed into both endogenous hypertriglyceridemia and hypercholesterolemia when compared to hepatoma-free (normal) rats fed the same diet. The hypercholesterolemia was due to an elevation (3.2 fold) in the very low-density lipoprotein plus low-density lipoprotein (VLDL + LDL)-cholesterol (Ch) level. The high-density lipoprotein (HDL)-Ch level was slightly but significantly decreased. These lipoprotein changes in hepatoma-bearing rats resulted in a marked (4.5 fold) increase in the atherogenic index (AI, (VLDL + LDL)-Ch/HDL-Ch) in comparison with that of tumor-free rats. The dietary additions of 1.2% Met, 1.2% Cys, and a combination of 1.2% Met and 2.5% Gly significantly suppressed the hepatoma-induced increase in (VLDL + LDL)-Ch with no influence on the hepatoma-induced decrease in HDL-Ch, leading to a noticeable fall in AI. These results indicate that hepatoma-bearing rats are useful as an endogenously hyperlipidemic model and that some dietary amino acids are capable of improving hepatoma-induced hypercholesterolemia and abnormal serum lipoprotein profiles.