Weanling rats were fed respective diets diverse in protein source and content for a full week, and hepatic serine dehydratase (SDH) was examined for its gene expression and activity induction attendant on high protein intake. The protein sources used were three kinds of milk casein, codfish meat, and wheat gluten. The body weight gain (% aug-mentation/wk) increased with increasing protein intake and reached a plateau in both milk casein- and codfish meat-fed rats by protein intake above 2.5g/100g BW/d; however, the body weight gain continued to increase albeit at a slower rate in wheat gluten-fed rats. Quite similar tendencies were also seen in nitrogen balance. The ascent of SDH activity induction and its causal gene expression were characterized as codfish meat>milk casein>>wheat gluten in order of response to protein intake near or more than 4g/100g BW/d. The difference in SDH gene expression among these dietary proteins was substantiated by a confirmation experiment in which six rats of each group were fed 25% or 50% protein diets under the same conditions as above. Hence, the quantity as well as quality of dietary protein turned out to have an influence on SDH gene expression.