One-month rats were randomized to a diet containing sorbitol (SOR) (54%), saccharose (SACCH) (54%) or that containing SOR (27%) and SACCH (27%). They were kept on the diets for 1 or 3 months. At the age of 2 and 4 months, the rats were returned to the routine diet of a vivarium. The experiments were terminated when the rats were aged 2, 4, and 7 months. In all seasons, the monthly diets containing 27% and 54% of SOR increased the serum activity of sortibol dehydrogenase (SDH) by several and tens of times. The 3-month diet produced the same effect. It suddenly turned out that the 54% SACCH diet also increased SDH activity, but to a lesser extent than a combination of 27 SOR and 27% SACCH, and by tens of times less than the 54% SOR diet. Comparison of three diets showed the same relationship between the increases in SDH activity in the liver. With excess dietary SOR, a very high increase was first found in serum and hepatic SOD activity by an induction mechanism.