Rats were fed a 21-percent protein diet, or isoenergetic amounts of 6-percent protein diets containing sucrose or starch, for 28 days. Although growth was retarded equally by both 6-percent protein diets, the pattern and degree of change in serum albumin concentration and liver composition was different, depending on the type of carbohydrate that was fed. Sucrose resulted in a greater fall in serum albumin compared with starch, and a larger liver, with a higher DNA, protein and fat content. Possible reasons are suggested for the lower serum albumin concentrations in the rats fed the 6-percent protein diet containing sucrose.