By the micro-bioassay method, quantitative studies were made on the increment of body weight and changes in free-lysine and threonine contents in the liver and plasm of rats, when they were fed on sucrose diet added with 0.3% DL-methionine, 0.36% DL-threonine and 0.1% L-tryptophane. The results of the experiment were as follows: (1) The weight gain and growth gain of rats decreased more when they were fed on 0.36% DL-threonine diet (Sth-group) than 0.3% DL-methionine diet (Sm-group). But those gain were increased when they were fed on 0.1% L-tryptophane diet (Str-group). (2) The contents of free-lysine and threonine in plasm and liver of rats were decreased more when they were fed on 0. 36% DL-threonine diet than 0.3% DL-methionine diet. And, those free amino acids were increased greatly when they were fed on 0.1% L-tryptophane diet. (3) The increment of body weight was the biggest when the free amino acid pattern showed that the contents of free-lysine decreased and threonine increased in the plasm and liver of rats being fed on 0.l% L-tryptophane diet.