Mature male and female rats were given ad libitum either control diet or low protein-high carbohydrate diets (starch or sucrose) for 4 weeks. Serum proteins, serum lipids and liver lipids were estimated. The adult females were more resistant to weight change than the males. Serum albumin concentrations in the females were higher than in the males. The males showed higher serum and liver lipid levels. There was a difference in serum protein and lipid levels between the males eating sucrose and those consuming starch, but no such differences were found in the females.