The purpose of this study was to see the effect of oral administration of reserpine (2mg/d) and tryptophan (40.35mg/d) on the serum amino acid concentrations and organ composition, food consumption, body weight, blood hematocrit(Hct) and hemoglobin(Hb) levels in Sprague-Dawley rats fed 6% or 20% casein diet. Any adverse effects of reserpine and tryptophan were not observed in animals, except that liver fat contents were increased in low protein group. In other words the administration of typtophan decreased liver fat contents in 6% casein and reserpine-treated 20% casein groups, but increased in reserpine-treated 6% casein group. But the low protein diet had significant adverse effects in animals. The 6% casein diet, therefore, had a tendency to decrease food consumption and body weight. The simillar tendency was shown in serum essential amino acid concentrations, organ weight and protein contents of liver and muscle. From the results, it would be safe to conclude that the oral administration of large deses of reserpine and tryptophan did not induce such a signifcant malnutrition as the low protein diet did.